filter
filter — noun
1. a piece of equipment or a layer of material that lets liquids or gases pass thro
a piece of equipment or a layer of material that lets liquids or gases pass through while trapping unwanted solid pieces inside it. Filters also block certain types of light, sound, or electrical signals.
Vikram replaced the water filter in his kitchen after noticing a strange taste in the tap water.
compound: water filter
The mechanic said the car's air filter was clogged with dust and needed changing.
compound: air filter
A coffee filter separates the ground beans from the liquid, giving you a clean cup of coffee.
collocation: coffee filter
Sound engineers use a special filter in the recording studio to remove background noise from the street.
Liang bought a new filter for his fish tank to keep the water clear and healthy for the fish.
filter + for + noun phrase
- water filter
- air filter
- coffee filter
- oil filter
- filter paper
- replace a filter
- clean a filter
Grammar Patterns
filter + for + noun
filter + made of/from + material
Usage Note
Often appears in compound nouns naming a specific type of filter (water filter, coffee filter, air filter). The material inside a filter is called the filter medium.
Common Mistakes
2. a coloured glass or plastic attachment that screws onto a camera and modifies th
a coloured glass or plastic attachment that screws onto a camera and modifies the colour, brightness, or quality of the light reaching the film or digital sensor
Élise attached a polarizing filter to her camera to reduce the strong glare coming off the lake.
A yellow filter can make the sky look darker and the clouds more dramatic in black-and-white photos.
Nellie forgot to remove the UV filter from her lens, and the indoor shots came out slightly dark.
compound: UV filter
Minh bought a set of screw-on filters for his new camera to experiment with landscape photography.
- UV filter
- polarizing filter
- neutral-density filter
- ND filter
- lens filter
- screw-on filter
- filter kit
- lens filter
more specific term for a camera filter that screws onto the lens
Grammar Patterns
[colour/type] + filter
filter + for + camera/lens
Usage Note
Common types include UV filters (protect the lens), polarizing filters (reduce reflections), and neutral-density filters (reduce the amount of light). Many photographers keep a UV filter on the lens permanently for protection.
Common Mistakes
3. a program, setting, or rule that examines information and decides what to keep o
a program, setting, or rule that examines information and decides what to keep or remove, for example by blocking unwanted emails or showing only search results that match certain conditions
Her email filter automatically moves messages from unknown senders into a junk folder.
compound: email filter
The job website has a salary filter that lets you see only positions within your budget.
collocation: salary filter
Parents often install a content filter on home computers to block websites that are not suitable for children.
compound: content filter
Adaeze applied a date filter to her spreadsheet so it showed only sales from the past month.
collocation: date filter
The search engine's safe-search filter prevents adult material from appearing in the results.
- spam filter
- email filter
- search filter
- content filter
- parental-control filter
- apply a filter
- remove a filter
Grammar Patterns
[noun] + filter
filter + for + [purpose]
Usage Note
Commonly appears in computing contexts. A spam filter sorts email, a search filter narrows results, and a parental-control filter restricts access to online content.
Common Mistakes
4. a digital tool inside a photo app or social-media platform that alters how a pic
a digital tool inside a photo app or social-media platform that alters how a picture looks by applying colour tones, smoothing skin, or adding decorative frames
Noor applied a vintage filter to her holiday photo before posting it on social media.
collocation: vintage filter
The beauty filter on that app makes everyone's skin look perfectly smooth.
compound: beauty filter
Yuki tried every filter available, but none of them made the sunset picture look any better.
Many apps now let you create your own custom filter and share it with friends.
custom filter
- vintage filter
- beauty filter
- apply a filter
- add a filter
- remove a filter
- custom filter
- photo filter
- Instagram filter
Grammar Patterns
apply/use + a filter
[app name] + filter
Usage Note
This sense is informal and very common on social media. Filters are often named after their effect: 'vintage', 'bright', 'monochrome', 'warmth'. The verb 'apply' is the most typical collocation.
5. the ability to stop yourself from saying something that might be rude, offensive
the ability to stop yourself from saying something that might be rude, offensive, or embarrassing. If someone has 'no filter', they say whatever comes to mind without thinking about how others might feel.
Talia has no filter — she told her boss exactly what she thought of his plan during the meeting.
idiomatic phrase: has no filter
When Ezra is tired, his filter disappears and he often says things he regrets later.
Grandpa speaks his mind without any filter, but somehow everyone loves his honesty.
prepositional phrase: without any filter
Cyrus wishes he had a better filter before making jokes at family dinners.
- have no filter
- lack a filter
- without a filter
- no social filter
- tact
the ability to say difficult things in a polite way; more formal than 'filter'
- self-censorship
deliberately stopping yourself from expressing something; more formal and deliberate
- bluntness
saying things directly without softening them
Grammar Patterns
have + no + filter
(someone's) + filter
Usage Note
Almost always used in the phrases 'have no filter', 'lack a filter', or 'without a filter'. The image is of a physical filter that would catch rude words before they come out of your mouth. This is an informal, metaphorical sense.
6. a green light in the shape of an arrow on a traffic-lights system that tells dri
a green light in the shape of an arrow on a traffic-lights system that tells drivers they may turn in that direction even when the main lights are red
Heloísa waited at the junction until the green filter arrow lit up, allowing her to turn right.
compound: filter arrow
The left filter at this intersection stays green for only ten seconds, so drivers must move quickly.
When the amber filter light appears, drivers should prepare to stop unless they have already entered the junction.
compound: filter light
Feng waited patiently behind three cars at the filter light before he could turn into the side street.
- filter arrow
- filter light
- filter junction
- green filter
- amber filter
- turn arrow
common term in American English for the same thing
- protected turn
a turn signal that stops oncoming traffic
Grammar Patterns
the + [colour] + filter
filter + light
Usage Note
This sense is mainly British English. In the US, this is called a 'turn arrow' or 'protected turn'. The filter is often a separate light below or beside the main traffic lights.
filter — verb
1. to move or pass slowly through a barrier, opening, or space. This can describe p
to move or pass slowly through a barrier, opening, or space. This can describe physical movement (people leaving a place bit by bit, light coming through a curtain) or information becoming known gradually over time.
The audience began to filter out of the theatre in small groups after the final scene ended.
phrasal verb: filter out (intransitive — people leaving)
Soft morning light filtered through the paper blinds and gently lit up the bedroom.
filter through [barrier] — light passing slowly
News of the accident slowly filtered back to the village, making everyone anxious.
filter back — information spreading slowly
New students filtered into the hall one by one, looking for empty seats near the back.
filter into [space] — people entering gradually
Reema waited for the details to filter through from the head office before making any announcements.
filter through from [source] — information becoming known
- filter through
- filter into
- filter out of
- filter back
- filter down
- gush
to flow out quickly and forcefully
Grammar Patterns
filter + through/into/out + noun phrase
filter + adverb of direction
Usage Note
Often used with a preposition (through, into, out of, back) that indicates the direction of slow movement. The subject is typically light, sound, people, or information — things that move gradually rather than all at once.
Common Mistakes
2. to pass a liquid or gas through a device in order to remove solid pieces or unwa
to pass a liquid or gas through a device in order to remove solid pieces or unwanted substances that are mixed in with it
The treatment plant filters all the drinking water through layers of sand and charcoal.
transitive: filter + object + through + medium
Indra always filters the used cooking oil through a cloth before storing it for later use.
transitive: filter + object + through + tool
Before you can drink it, the rainwater must be filtered to remove dirt and bacteria.
passive: be filtered to remove
This swimming-pool pump filters the water continuously, so it stays clean all summer.
The machine filters out all the dust particles from the air before releasing it back into the room.
phrasal verb: filter out + particle
- filter water
- filter air
- filter oil
- filter through cloth
- filter out impurities
- be filtered
- contaminate
to make something dirty or impure
Grammar Patterns
filter + noun phrase
filter + noun phrase + through + noun phrase
filter + noun phrase + out
filter + out + noun phrase
Usage Note
Can be used transitively ('filter the water') or with 'filter out' to emphasise the removal ('filter out impurities'). The passive form is very common ('is filtered', 'must be filtered').
Common Mistakes
3. to examine a collection of information, such as emails, files, or search results
to examine a collection of information, such as emails, files, or search results, and keep only the items that meet certain conditions while removing the rest
Christopher filters his inbox so that only messages from his team appear in his main view.
transitive: filter + direct object
The job board filters the listings by salary range, location, and years of experience.
filter + by + criteria
You can filter the spreadsheet to show only rows where the sales total is above five thousand.
Adaeze filtered out all the duplicate entries before running the final report for her manager.
phrasal verb: filter out + object
The app lets you filter for vegan restaurants within two kilometres of your current location.
filter + for + criterion
- filter data
- filter results
- filter emails
- filter by
- filter for
- filter out duplicates
- sort
rearranges items by a rule but does not remove them
- narrow down
reduces a set of options by applying criteria
- sift
examines items closely to separate wanted from unwanted
Grammar Patterns
filter + noun phrase
filter + noun phrase + out
filter + out + noun phrase
filter + for + criterion
Usage Note
Can be followed by 'by' (filter by price), 'for' (filter for specific items), or 'out' (filter out unwanted data). In spreadsheet software, 'filter' is a standard feature that hides rows that do not meet the criteria.
Common Mistakes
filter out
phrasal verbto remove something unwanted from a group or mixture by passing it through a filter or by applying a selection rule
The water purifier filters out harmful chemicals before the water reaches the tap.
The recruiter filtered out all applicants who did not have a valid driver's license.
filter through
phrasal verbto pass slowly through something, or to become known gradually as information spreads through a group or organisation
It took several days for the news of the merger to filter through to the junior staff.
Sunlight filtered through the heavy clouds and lit up the valley below.
Word family
- filtrationnounB2
- filteredadjectiveB1
- unfilteredadjectiveB2
- filterableadjectiveC1
- infiltrateverbC1
- infiltrationnounC1
Synonym discussion
Sense: noun/1
All four words describe devices that separate materials, but they differ in how fine the separation is and what they are used for. A filter uses a porous material (paper, sand, charcoal) to trap tiny particles that a sieve would let through — coffee grounds need a filter, while pasta needs a colander. A sieve or strainer uses a mesh and separates by particle size; a colander is a large bowl with holes used in the kitchen for draining. A purifier goes further by removing chemical contaminants or microorganisms, not just physical solids. For example: 'Use a strainer to wash the rice, but a filter to remove bacteria from the water.'
Common collocations
Etymology
The word 'filter' comes from Latin 'filtrum', which meant 'felt' — a thick, matted fabric used in ancient times to strain liquids. The word entered English through Old French 'filtre' in the 15th century, first used for the cloth itself and later for any device that separates substances. The metaphorical senses (information filtering, self-restraint) developed in the 20th century with the rise of computing and psychology.