flag
flag — noun
1. a square or oblong sheet of fabric marked with a distinctive design, used as the
a square or oblong sheet of fabric marked with a distinctive design, used as the official emblem of a country, a group of people, or an organization.
Tariro hung a Japanese flag outside her window during the World Cup.
flag + of [country]
The stadium was covered with flags from more than two hundred nations.
Soldiers stood at attention while the national flag was raised at dawn.
passive: be raised (of a flag)
Every ship in the harbour flew a bright red signal flag for the holiday.
The Olympic flag has five coloured rings on a white background.
- national flag
- raise a flag
- lower a flag
- fly a flag
- wave a flag
- under the flag of
- flag of convenience
Grammar Patterns
flag + of + country/organization
Usage Note
National flags are often paired with verbs like raise, lower, fly, wave, and fold. Countries also use their flag as a symbol in contexts such as war, diplomacy, and sport.
Common Mistakes
2. in American football, a small yellow cloth square that the referee throws onto t
in American football, a small yellow cloth square that the referee throws onto the field to show that a player has broken a rule.
The referee threw a yellow flag when the defender grabbed the receiver's arm.
throw a flag for [violation]
Shanti knew her team would lose yardage when she saw the flag on the grass.
A flag for holding pushes a team back ten yards from the foul spot.
flag for [violation] +yardage consequence
The home crowd booed when a flag halted their team's best play.
- throw a flag
- yellow flag
- flag on the play
- flag for pass interference
Grammar Patterns
throw a flag
flag for + [violation type]
Usage Note
In American football, the yellow penalty flag is a physical cloth. The verb sense (verb/5) describes the official's action of throwing it.
3. something that shows a possible problem, danger, or cause for concern, especiall
something that shows a possible problem, danger, or cause for concern, especially before the problem becomes serious.
A sudden drop in sales was a red flag for the company's management team.
red flag — metaphor for a serious warning
Brooke noticed several warning flags in the contract before she signed it.
Teachers learn to spot flags that may show a child is struggling at home.
The lack of receipts raised a red flag during the tax audit last spring.
raise a red flag — collocation
- red flag
- raise a red flag
- warning flag
- flag of concern
- warning sign
more general; less metaphorical than red flag
- indicator
neutral term; can be positive or negative
- alarm bell
stronger; suggests an immediate danger
Grammar Patterns
red flag
flag for + [concern]
Usage Note
Red flag is the most common form. It is often used in business, healthcare, and security contexts to describe early indicators of risk.
Common Mistakes
4. a flat piece of stone, usually square or rectangular, used to cover floors, path
a flat piece of stone, usually square or rectangular, used to cover floors, paths, patios, or other outdoor surfaces.
The garden path was made of grey flags that had been there for decades.
Dario laid new sandstone flags across the patio behind his house last weekend.
lay + flags — construction collocation
Moss had grown between the old flags in the courtyard of the cathedral.
The kitchen floor was covered with large uneven flags of local stone.
flags of + [stone type]
- flagstone
- lay flags
- stone flags
- sandstone flags
- granite flags
- flagstone
the full form; more formal and technical
- paving stone
general term for any stone used in paving
- slab
larger and thicker; used for concrete or stone surfaces
Grammar Patterns
flagstone
flag + [stone type]
Usage Note
Often shortened from flagstone. The plural flags is very common when describing paved areas. Not to be confused with the cloth senses.
5. a waterside plant belonging to the iris family, with long sword-shaped leaves an
a waterside plant belonging to the iris family, with long sword-shaped leaves and showy flowers that are usually yellow, blue, or purple.
Yellow flags grew wild along the edge of the stream behind the old mill.
flag + colour + location (plant sense)
Eleni planted blue flags near the pond in her grandmother's cottage garden.
The long green leaves of the flag rose from the damp soil like swords.
In early summer, purple flags bloom across the marshy area of the nature reserve.
passive: bloom + location (marshland) — typical habitat
- yellow flag
- blue flag
- flag iris
- flag plant
- water flag
- iris
the broader botanical category that includes flags
- sweet flag
a related waterside plant (Acorus calamus), not a true iris
Usage Note
This sense is uncommon in everyday conversation. It mainly appears in gardening and nature writing. Yellow flag (Iris pseudacorus) is the most common type mentioned.
flag up
phrasal verbto draw someone's attention to something important or that needs to be dealt with, especially in a work or formal context.
The accountant flagged up several errors in last month's expense reports before the audit.
Could you flag up any problems with the new software before the launch on Friday?
flag down
phrasal verbto signal to a vehicle or its driver to stop, usually by raising or waving your arm or hand.
The tourist flagged down a taxi outside the train station after waiting for twenty minutes.
A police officer flagged down the truck because one of its lights was not working.
fly the flag
idiomto represent your country, organization, or group with obvious pride and support, especially when you are away from home.
The small bakery flies the flag for traditional French baking in the middle of London.
A group of Taiwanese students flew the flag at the international science fair by winning three gold medals.
keep the flag flying
idiomto continue to represent and support your country, group, or tradition even when things are difficult.
Even though the theatre company had very little money, they kept the flag flying with one show a month.
Grandpa keeps the flag flying for the old recipes by cooking them every Lunar New Year.
red flag
idioma clear sign that something is wrong, dangerous, or likely to cause serious trouble.
When the builder asked for full payment in cash upfront, that was a red flag for the family.
A sudden change in a child's eating habits can be a red flag for teachers and parents.
wave the flag
idiomto show strong, sometimes exaggerated, support for your country or group, especially in public.
Politicians often wave the flag during election campaigns to win patriotic votes.
Cyrus was happy to wave the flag for his hometown team at every away game.
To publicly demonstrate loyalty or support for a country, group, or belief, often to inspire others.
At the parade, Maya waved the flag by wearing her national colors.
The company showed the flag at the trade fair with a big booth.
Something that is certain to cause a very angry reaction from someone.
Mentioning his ex-wife was like waving a red flag in front of a bull.
Bringing up politics at dinner is like waving a red flag in front of a bull.
flag — verb
1. to put a physical or digital mark on something so that it can be found or identi
to put a physical or digital mark on something so that it can be found or identified more easily later among other things.
Hao flagged the important pages in the report with small yellow sticky notes.
flag + noun + with [tool]
The librarian flagged every book that had not been returned by the due date.
Roya flagged the emails from her manager so she could read them first.
Brandon flagged the sections of the proposal that still needed revision before the board meeting.
passive structure: flagged + for + purpose
Each item on the list was flagged as urgent or routine by the assistant.
flag + as + category
- flag for review
- flag as important
- flag with a note
- flagged items
- flagged emails
Grammar Patterns
flag + noun phrase + for + purpose
flag + noun phrase + as + category
Usage Note
This sense is about personal organisation — you flag something to help yourself find it later. Distinguish from verb/3, where you flag something to warn others about a problem.
Common Mistakes
2. to mark computer data or an item in a system with a true/false value so that it
to mark computer data or an item in a system with a true/false value so that it can be identified, filtered, or processed in a specific way by the program.
The security system flags any file that contains suspicious code for the team to inspect.
flag + noun + for + [action]
Hyun wrote a script that flags user accounts that have been inactive for six months.
The payment system flags transactions over ten thousand dollars for manual review.
Each database record is flagged as active or archived by the program.
passive: flagged as + [state]
- flagged as active/inactive
- flagged for review
- flagged records
- flagged transactions
- flagged entries
- tag
can add any type of metadata, not just boolean values
- label
more general; used in both programming and everyday language
- set a flag on
more technical; describes the actual programming operation
Grammar Patterns
flag + noun + as + boolean value
flag + noun + for + processing
Usage Note
Closely related to verb/1 in the action of marking, but this sense specifically involves a binary (true/false) or categorical value in a computing context. Frequently passive: items are flagged by the system, not by a person.
3. to tell someone about something important or problematic so that they can take a
to tell someone about something important or problematic so that they can take action, especially before it becomes a bigger issue.
The school nurse flagged the student's allergy to the new teacher before the class trip.
flag + noun + to + recipient
A neighbour flagged the broken streetlight to the city council after the accident.
The audit report flagged several financial problems that needed immediate attention.
Gita flagged that the shipping address was wrong before the package went out.
flag + that-clause
Users can flag offensive comments on the website for moderators to review.
flag + noun + for + [action by recipient]
- flag a problem
- flag an issue
- flag concerns
- flag to management
- flag for attention
- flag up
Grammar Patterns
flag + noun + to + person
flag + noun + for + reason
flag + that-clause
Usage Note
Distinguish from verb/1: flagging a problem (verb/3) means drawing others' attention so they can act; flagging a page (verb/1) is for your own future reference. British English also uses flag up (phrasal verb) for this sense.
Common Mistakes
4. to become physically tired, lose strength or energy, or start to decline in qual
to become physically tired, lose strength or energy, or start to decline in quality, interest, or effectiveness over time.
Eli's energy began to flag after walking for eight hours under the hot desert sun.
Nora's interest in the project flagged when she saw how much paperwork was involved.
subject [interest/enthusiasm/energy] + flag — typical subject pattern
The conversation flagged after everyone ran out of new things to talk about.
flag — intransitive, describing a social situation
Public support for the new law flagged as more people learned about the cost.
- energy flags
- spirits flag
- interest flags
- enthusiasm flags
- conversation flags
- flag under pressure
- strengthen
the opposite direction of change
- pick up
informal; to recover lost energy or pace
Grammar Patterns
flag + adverb of degree
flag + under + pressure
Usage Note
Intransitive only — you never flag something in this sense. The subject is typically energy, enthusiasm, interest, conversation, spirits, or support. Describes a gradual process, not a sudden stop.
Common Mistakes
5. (in sports, especially American football) for an official to raise or throw a fl
(in sports, especially American football) for an official to raise or throw a flag to signal that a player has broken a rule, or to penalize a player for doing so.
The referee flagged the defender for holding the receiver's jersey during the play.
flag + player + for + [violation]
The official flagged the runner for starting before the starting gun sounded.
Élise was flagged for a dangerous tackle during the championship semifinal match.
passive: be flagged for [violation]
The linesman flagged as soon as the forward passed the last defender.
intransitive: flag (no object) — official's action
- flag a player
- flagged for a foul
- flagged offside
- flagged for holding
- flagged for pass interference
- penalize
broader; applies to any sport and can mean giving a penalty without using a flag
- call a penalty on
describes the refereeing decision, not specifically the flag gesture
Grammar Patterns
flag + player
flag + player + for + violation
flag (no object)
Usage Note
Can be transitive (the official flags the player) or intransitive (the official simply flags, without naming who). In American football, throwing a yellow flag is the physical act; flagging is the official's decision to do so.
Word family
Synonym discussion
Sense: noun/1
All five words describe pieces of cloth used as symbols, but they differ in use and register. Flag is the general everyday word for any country's or organization's emblem on cloth — you fly a flag, wave a flag, or salute a flag. Banner originally described a long cloth hung vertically, often at rallies or festivals; today it also refers to web graphics (a banner ad). Ensign is a formal, nautical term: a ship flies its national ensign to show its country of registration. Standard is a military or ceremonial flag, often carried on a pole in parades or by cavalry units; it also refers metaphorically to what an organization stands for ('uphold the standard'). Pennant is a long, narrow triangular flag, common in sports (a championship pennant) or on ships. In daily use, flag is correct in nearly all situations; the others add specific context. For example: 'The embassy flies the national flag every day,' but 'the ship changed its ensign when it entered foreign waters.'
Common collocations
Etymology
The noun flag has two separate origins. The common meaning 'piece of cloth as a symbol' probably came from early modern English, possibly imitating the way a cloth flaps in the wind (like the obsolete word flag meaning 'to flutter'). The 'flagstone' sense (noun/4) comes from Old Norse flaga, meaning 'a slab of stone.' The 'iris' sense (noun/5) may come from a different root related to reeds or rushes. The verb meanings all developed from the noun in the 1800s: 'to mark with a flag' (verb/1), 'to warn' (verb/3), and 'to become weak' (verb/4) — the last of which may come from an unrelated older word flag meaning 'to droop or hang down.'