fluid

American  

[floo-id] / ˈflu ɪd /

noun

• fluids
  plural

1. a substance, as a liquid or gas, that is capable of flowing and that changes its shape at a steady rate when acted upon by a force tending to change its shape.

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adjective

1. pertaining to a substance that easily changes its shape; capable of flowing.

2. consisting of or pertaining to fluids.

3. changing readily; shifting; not fixed, stable, or rigid.

   fluid movements.

4. convertible into cash.

   fluid assets.

fluid British  

/ ˈfluːɪd /

noun

1. a substance, such as a liquid or gas, that can flow, has no fixed shape, and offers little resistance to an external stress

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adjective

1. capable of flowing and easily changing shape

2. of, concerned with, or using a fluid or fluids

3. constantly changing or apt to change

4. smooth in shape or movement; flowing

fluid Scientific  

/ flo̅o̅′ĭd /

1. A state of matter, such as liquid or gas, in which the component particles (generally molecules) can move past one another. Fluids flow easily and conform to the shape of their containers.

2. See also state of matter viscosity

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fluid Cultural  

1. In physics, a substance that flows — usually a liquid or a gas.

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Synonym Usage

See liquid.

Other Word Forms

Derived Forms

• fluidness
  noun
• nonfluid
  noun
• fluidal
  adjective
• unfluid
  adjective
• fluidally
  adverb
• fluidly
  adverb
• nonfluidly
  adverb

Inflected Forms

Nouns

• fluids
  plural

Etymology

Origin of fluid

First recorded in 1595–1605; from Latin fluidus, equivalent to flu(ere) “to flow” + -idus adjective suffix; see -id ⁴

Explanation

Something that is unstable or subject to change can be described as fluid. The fluid political situation in a particular country makes it unsafe to travel there, with the constant possibility of a violent uprising. A liquid is a fluid — something that flows easily when poured — although gases can also be called fluid. When your doctor told you to drink lots of fluids to help your cold symptoms, she probably meant things like water or orange juice, not root beer floats. If a movement is smooth, it can also be described as fluid. You have to make fluid arm movements in ballet so you look graceful.

Example Sentences

See Examples For:

fluid fluids

“Markets are increasingly pricing gradual de-escalation, although geopolitical developments remain fluid and vulnerable to renewed tensions,” analysts at brokerage Kotak Neo say.

From The Wall Street Journal ● Sep. 23, 2026

"They work by absorbing fluid from superficial spots while creating a protective barrier that discourages picking," she explains.

From BBC ● Sep. 21, 2026

"Superfluid helium is what is known as a quantum fluid, in which the individual helium atoms lose their identity, and which does not tolerate any impurities within it."

From Science Daily ● Sep. 18, 2026

There are stories in ballet, yes, but the allure is in the fluid possibilities of the human body and the expression therein.

From The Wall Street Journal ● Sep. 17, 2026

He’s still strong, in decent shape; his moves, still fluid.

From "Black Brother, Black Brother" by Jewell Parker Rhodes

The company sells chemicals used in energy production called completion fluids, mainly to deepwater producers in the North Sea and off the coast of Brazil and the U.S.

From MarketWatch ● Sep. 19, 2026

Scientists assumed that the collision was so energetic that the rocky bodies could effectively be treated like fluids.

From Science Daily ● Sep. 11, 2026

The problem was part of the Navier-Stokes equations, external, which concern how fluids move.

From BBC ● Sep. 8, 2026

Geology agency head Lana Saria said "seismic activity indicates the movement or release of volcanic fluids within the volcanic system".

From Barron's ● Sep. 6, 2026

“It’s healthier to drink all your fluids ten minutes before you eat,” he counters.

From "Dry" by Neal Shusterman and Jarrod Shusterman

Related Words

• flexible
• shifting
• unsettled
• unstable