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.

---

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

---

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

---

fluid Cultural  

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

---

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

The Middle East situation remains fluid, with little progress in talks to reopen the Strait of Hormuz.

From The Wall Street Journal ● Aug. 17, 2026

But Barca's opening bid for a player out of contract next summer was only £38.5m but the situation remains fluid.

From BBC ● Aug. 14, 2026

In commentary published Thursday, Buchbinder explains that the stock market’s relationship with bonds is fluid.

From MarketWatch ● Aug. 14, 2026

In more open areas around the brain, including the space near the surface between the skull and the brain, the water-like fluid travels at a few microns per second.

From Science Daily ● Aug. 13, 2026

“Erm...brain fluid, I think. We had a pressure leak on the last mission. But that’s plugged now. And the officer lived. Down a few IQ points, but alive, and he can still take liquids.”

From "Artemis Fowl" by Eoin Colfer

The process of hydraulic fracturing ekes out oil from older wells, and involves cracking the bedrock several thousand feet below the seafloor by injecting chemical fluids with intense pressure.

From Los Angeles Times ● Aug. 14, 2026

Briny fluids likely helped drive at least some of that chemistry.

From Science Daily ● Aug. 8, 2026

Ebola is spread by contact with bodily fluids and causes a haemorrhagic fever.

From Barron's ● Aug. 7, 2026

Zoo staff provided ventilation and water to cool her down, and later administered subcutaneous fluids, liver tonics and vitamins.

From BBC ● Aug. 4, 2026

But I have an organ that moves fluids around in me.

From "Pet" by Akwaeke Emezi

Related Words

• flexible
• shifting
• unsettled
• unstable