fluid
Americannoun
adjective
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pertaining to a substance that easily changes its shape; capable of flowing.
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consisting of or pertaining to fluids.
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changing readily; shifting; not fixed, stable, or rigid.
fluid movements.
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convertible into cash.
fluid assets.
noun
adjective
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capable of flowing and easily changing shape
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of, concerned with, or using a fluid or fluids
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constantly changing or apt to change
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smooth in shape or movement; flowing
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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.
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See also state of matter viscosity
Synonym Usage
See liquid.
Other Word Forms
Derived Forms
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.
Vocabulary lists containing fluid
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Early studies showed that the shuttle-delivered trontinemab reached concentrations in the brain’s fluid that are eight times higher than standard antibodies, with much more uniform distribution around the brain.
From Barron's • Jun. 3, 2026
"Possibly, this is due to their more egalitarian social systems. Bonobos appear to live together in more fluid relationships, with social bonds that transcend group boundaries, something we rarely see in chimpanzees," explains Van Leeuwen.
From Science Daily • May 31, 2026
Reading from nose to tail, these coves generate the fluid character lines along the doors that bend toward each other, per Bernoulli.
From The Wall Street Journal • May 30, 2026
The prostate sits just below the bladder and has a vital role in male anatomy as it helps make part of the seminal fluid and can affect the flow of urine.
From BBC • May 28, 2026
He had the notion that everyday substances like air, or water, or mercury were mingled with a much finer substance, a fluid which filled all the gaps and prevented the existence of a vacuum.
From "The Scientists" by John Gribbin
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
