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

“We’re looking for places that we can push this fluid, should it fail, and try to prevent it from getting into our storm drains or river channels, and ultimately into the ocean,” he said.

From The Wall Street Journal • May 23, 2026

The goal was to determine whether GLP-1 could be measured in joint fluid and how those levels compared with concentrations found in the blood.

From Science Daily • May 22, 2026

“I am very sympathetic with voters who want to take their time to make their decision in this very fluid election,” she said.

From Los Angeles Times • May 21, 2026

However, "the Iran situation remains highly fluid," she added.

From Barron's • May 21, 2026

Two singed pink nodules drop into a glass of fluid.

From "The Last Cuentista" by Donna Barba Higuera

Related Words

• flexible
• shifting
• unsettled
• unstable