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
Related Words
See liquid.
Other Word 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.
The crew is set to carry out numerous scientific projects in life sciences, materials science, fluid physics and medicine.
From Barron's • May 24, 2026
"It was about getting through that tough period rather than looking to punish bad bowling or really try to get on top of the bowlers. Once I got through that I was more fluid."
From BBC • May 24, 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
And what qualifies as a TV movie in 2026, when TV and film mediums are beyond fluid?
From Los Angeles Times • May 21, 2026
She was a longtime colleague of Farmer’s, and she had questions about treating someone with hydrocephalus—an abnormal amount of fluid in the brain’s ventricles, or cavities—caused by a parasite.
From "Mountains Beyond Mountains" by Tracy Kidder and Michael French
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.
