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; 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

England forward Hemp said she was "loving" her "more fluid" role up front and gave an insight into what they have been doing on the training ground.

From BBC • May 6, 2026

Either way, the end result was a fluid style of football that was practically impossible to stop and resulted in Barcelona claiming 14 trophies during Guardiola's time at the helm.

From BBC • May 6, 2026

“It’s like you’re drowning. The lungs are leaky, so the fluid fills up in the lungs.”

From Los Angeles Times • May 4, 2026

Still, the landscape remains fluid, with structural challenges for both parties.

From Barron's • May 3, 2026

Others think it has to do with the primal fluid of the universe.

From "Jeremy Thatcher, Dragon Hatcher" by Bruce Coville

Related Words

• flexible
• shifting
• unsettled
• unstable