fluid

American  

[floo-id] / ˈflu ɪd /

noun

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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Related Words

See liquid.

Other Word Forms

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

Etymology

Origin of fluid

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

Example Sentences

Her husband took her to hospital, where doctors performed a CT scan which picked up free fluid in the abdominal area.

From BBC • Apr. 8, 2026

With specialized imaging tools, the team found that cells actively generate directional fluid flows, which they compare to atmospheric rivers.

From Science Daily • Apr. 1, 2026

This month, the zoo announced Tina was suffering from an infection and abnormal buildup of fluid in her uterus.

From Los Angeles Times • Mar. 31, 2026

Watch as the fluid camerawork makes her kills look nastier, and the preposterous script allows her to outwit her foes, even with the cards stacked against her at every turn.

From Salon • Mar. 29, 2026

If you can create the right framework, all of a sudden, engaging in the kind of fluid, effortless, spur-of-the-moment dialogue that makes for good improv theater becomes a lot easier.

From "Blink" by Malcolm Gladwell

Related Words

• flexible
• shifting
• unsettled
• unstable