fluid

1 of 3

adjective

flu·​id ˈflü-əd 

1

a

: having particles that easily move and change their relative position without a separation of the mass and that easily yield to pressure : capable of flowing

… a long screw that forces the fluid chocolate through fine openings.

—Technical Survey

b

: subject to change or movement

boundaries became fluid

2

: characterized by or employing a smooth easy style

the ballerina's fluid movements

fluid recitation of his lines

3

a

: available for various uses

a fluid computer program

b

: liquid sense 4

fluid assets

fluidly adverb

fluidness noun

fluid

2 of 3

noun (1)

: a substance (such as a liquid or gas) tending to flow or conform to the outline of its container

fluidal

ˈflü-ə-dᵊl 

adjective

fluidally

ˈflü-ə-dᵊl-ē 

adverb

fluidlike

ˈflü-ə-dᵊl-ˌlīk 

adjective

fluidness

3 of 3

noun (2)

flu·​id·​ness

plural -es

: the quality or state of being fluid : fluidity

Synonyms of fluid

Adjective

• liquid
• flowing

Examples of fluid in a Sentence

Adjective

a substance in a fluid state

warm the jam until it is fluid, then spread it over the cake

Noun (1)

Please check the fluids in the car's engine.

She needs to drink plenty of fluids.

Fluid leaked from the car's engine.

a bottle of yellow fluid

Recent Examples on the Web

Adjective

Brazil’s team, meanwhile, decamped to Orlando, Florida, where Laitano affixed players with sweat-collection patches and analyzed their fluid and electrolyte loss during workouts to concoct a hydration regimen for each person. — Nancy Walecki, The Atlantic, 2 July 2026

His backpedal in drop coverage for a player his size is incredibly fluid. — Sam Vecenie, New York Times, 2 July 2026

Noun

To keep cool, Hillman recommends that people drink plenty of fluids, while avoiding sugary or caffeinated drinks. — Eduardo Cuevas, USA Today, 1 July 2026

That process can lead to heat exhaustion or heat stroke, and the mix of extreme heat, high humidity and low fluid intake can trigger organ failure in as little as an hour, according to the Mayo Clinic. — Hanna Wickes, Charlotte Observer, 1 July 2026

Word History

Etymology

Adjective and Noun (1)

French or Latin; French fluide, from Latin fluidus, from fluere to flow; akin to Greek phlyzein to boil over

First Known Use

Adjective

1603, in the meaning defined at sense 1a

Noun (1)

1661, in the meaning defined above

Phrases Containing fluid

• amniotic fluid
• cerebrospinal fluid
• correction fluid
• drilling fluid
• fluid dram
• fluid mechanics
• fluid ounce
• gender-fluid
• lighter fluid
• seminal fluid
• serosal fluid
• serous fluid
• synovial fluid
• tissue fluid
• working fluid

Rhymes for fluid

• druid
• superfluid

Kids Definition

fluid

1 of 2 adjective

flu·​id ˈflü-əd 

1

a

: capable of flowing like a liquid or gas

b

: likely or tending to change or move

2

: showing a smooth easy style

fluid movements

fluidly adverb

fluidness noun

fluid

2 of 2 noun

: a substance tending to flow or take the shape of its container

liquids and gases are fluids

fluidlike

-ˌlīk 

adjective

Etymology

Adjective

from French fluide or Latin fluidus, both meaning "fluid, able to flow," from Latin fluere "to flow" — related to affluent, fluent, flush entry 2, influence, superfluous

Medical Definition

fluid

1 of 2 adjective

flu·​id ˈflü-əd 

: having particles that easily move and change their relative position without a separation of the mass and that easily yield to pressure : capable of flowing

fluid

2 of 2 noun

: a substance (as a liquid or gas) tending to flow or conform to the outline of its container

specifically : one in the body of an animal or plant see cerebrospinal fluid, seminal fluid