dam

dam — noun

1. a strong wall or barrier placed across the path of a river or stream to hold bac

1.nounB1
Definition

a strong wall or barrier placed across the path of a river or stream to hold back the current, forming a lake or reservoir that can supply water for farming or produce electric power

Example

The government built a new dam across the Yellow River to supply water to nearby farms.

collocation: build a dam across [river]

After heavy rain, engineers checked the dam for cracks to prevent flooding.

Common collocations
  • build a dam
  • construct a dam
  • hydroelectric dam
  • dam wall
  • dam broke
  • behind the dam
  • upstream of the dam
Synonyms
  • barrier

    a general term for any structure that blocks movement; less specific than dam

  • dike

    a wall built to prevent flooding from the sea, usually along a coast rather than across a river

  • weir

    a low dam built across a river to control water level, smaller and simpler than a dam

Grammar Patterns

a dam

the dam

Common Mistakes

The dam exploded during the storm.
The dam broke during the storm.
Dams break or collapse; they do not explode in natural disaster contexts.

2. a mound of branches, mud, and stones that beavers build across a narrow stream t

2.nounB1
Definition

a mound of branches, mud, and stones that beavers build across a narrow stream to create a calm pond where they can live and store food

Example

The beavers built their dam across a small stream behind Bao's house.

collocation: build a beaver dam across [stream]

When the water level dropped, hikers could see the beaver dam made of branches and mud.

material: branches, mud

Common collocations
  • beaver dam
  • build a dam
  • behind the beaver dam
Synonyms
  • beaver lodge

    the beaver's home structure, usually built within the pond created by the dam

Grammar Patterns

a beaver dam

Usage Note

Beaver dams are typically much smaller than human-built dams and are made from natural materials. They play an important role in creating wetland ecosystems.

3. the mother of an animal, used especially for horses, cows, and other domestic an

3.nounC1
Definition

the mother of an animal, used especially for horses, cows, and other domestic animals that give birth to young

Example

The horse breeder recorded the dam's name along with the foal's birth date in the registry.

collocation: dam + foal in breeding context

This prize-winning calf came from a dam that had won several national competitions.

Common collocations
  • dam's offspring
  • dam and sire
  • record of the dam
Synonyms
  • mother

    the general term for a female parent in any species; less technical than dam

Antonyms
  • sire

    the male parent of an animal, especially a horse or domestic animal

Grammar Patterns

the dam

dam + offspring

Usage Note

Frequently used in animal breeding records. Distinguish from sire, which refers to the male parent. The term dam is most common in horse and cattle breeding contexts.

Common Mistakes

The dam of the puppy was a golden retriever.
The mother of the puppy was a golden retriever.
Dam is used for livestock and horses; for pet animals like dogs, mother is more common.

4. a thin flexible sheet, usually made of latex, placed over the mouth or teeth as

4.nounC1
Definition

a thin flexible sheet, usually made of latex, placed over the mouth or teeth as a barrier — dentists use it to isolate a single tooth during work on it, and it can also serve as protection during oral sex to lower the chance of infections

Example

The dentist placed a small rubber dam around Talia's tooth before starting the filling.

dental context: rubber dam around [tooth]

Noor bought dental dams at the pharmacy for protection during oral sex.

sexual health context: dental dam for protection

Common collocations
  • dental dam
  • rubber dam
  • use a dam
  • place a dam
  • dental dam for protection
Synonyms
  • rubber dam

    more common term in dentistry; refers to the same thin sheet

  • oral dam

    alternative name used in sexual health contexts

Grammar Patterns

a dental dam

use a dam

Usage Note

In dental contexts, also called a rubber dam. In sexual health contexts, the same type of sheet is often called a dental dam or oral dam. The colour and flavouring may differ between dental and sexual health products.

Common Mistakes

He used a dental dam for the tooth extraction.
The dentist used a rubber dam during the root canal treatment.
Dental dam is the preferred term in both medical and sexual health contexts; rubber dam is more common in dentistry.

5. a unit of length equal to ten meters, written as dam in abbreviations — one deka

5.nounC1
Definition

a unit of length equal to ten meters, written as dam in abbreviations — one dekameter is about 32.8 feet

Example

Using her GPS device, the surveyor noted that the field boundary sat 12 dam from the edge of the main road.

abbreviation usage: dam = dekameter

The surveyor recorded the distance between the two boundary markers as 12 dam on her field map.

surveying context: dam on a field map

Grammar Patterns

dam (abbreviation)

Usage Note

The abbreviation dam for dekameter is most common in technical and scientific writing. In everyday conversation, people usually say ten meters rather than one dekameter. The abbreviation uses the same letters as the noun dam, so context must clarify the meaning.

Idioms

Dam, (Carl Peter) Henrik

idiom

A Danish biochemist (1895–1976) who discovered vitamin K in 1934 and later shared the 1943 Nobel Prize in Physiology or Medicine for this discovery. His research helped explain how the body produces proteins that make blood clot properly.

Like Henrik Dam, many scientists make important discoveries while studying everyday health problems.

The biology textbook mentioned Henrik Dam's Nobel Prize for uncovering vitamin K.

dam — verb

Word family

  • dammed
    adjectiveC1
  • damming
    adjectiveC1
  • dam up
    phrasal verbC1
  • damless
    adjectiveC2

Synonym discussion

Sense: noun/1

These words all describe structures that block or control water, but they differ in purpose and location. A dam is built across a river to create a reservoir or generate power — it blocks the entire flow. A dike is a wall constructed along a coastline or riverbank to prevent flooding from the sea, not across the flow. A levee is similar to a dike but specifically refers to an embankment along a river, often built from earth, to contain high water levels. A weir is a low overflow dam built across a river to control the water level; water flows over its top rather than being fully blocked. A barrier is the most general term — any structure that prevents movement, not limited to water contexts. For example: 'The government built a dam to supply water to the city,' but 'The town raised the dike after the storm surge.' Use dam when water is being stored or fully blocked; use weir when water is meant to flow over the top; use dike or levee when the goal is flood protection along a shoreline.

dam ↗dikeleveeweirbarrier ↗

Common collocations

Nouns

Phrases

  • build a dam across
  • dam up
  • behind the dam

Prepositions

Etymology

Proto-GermanicOld EnglishMiddle EnglishEnglish

The noun dam meaning 'a barrier to hold back water' comes from Middle English damme, which developed from Old English *damm (a barrier), related to Old Frisian damm and German Damm. The word has Germanic origins. The sense 'mother of an animal' comes from a different root — it is a variant of dame, which entered English from Old French dame ('lady, mother'), derived from Latin domina ('mistress of a house'). These two meanings are unrelated but happen to share the same spelling in modern English. The abbreviation dam for dekameter is a modern shortening of the metric prefix deca- plus meter.