[ floo-id ]
See synonyms for fluid on Thesaurus.com
  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.

  1. pertaining to a substance that easily changes its shape; capable of flowing.

  2. consisting of or pertaining to fluids.

  1. changing readily; shifting; not fixed, stable, or rigid: fluid movements.

  2. convertible into cash: fluid assets.

Origin of fluid

First recorded in 1595–1605; from Latin fluidus, equivalent to flu(ere) “to flow” + -idus adjective suffix; see -id4

synonym study For fluid

2. See liquid.

Other words from fluid

  • flu·id·al, adjective
  • flu·id·ly, flu·id·al·ly, adverb
  • flu·id·ness, noun
  • non·flu·id, noun
  • non·flu·id·ly, adverb
  • un·flu·id, adjective

Words that may be confused with fluid

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use fluid in a sentence

British Dictionary definitions for fluid


/ (ˈfluːɪd) /

  1. a substance, such as a liquid or gas, that can flow, has no fixed shape, and offers little resistance to an external stress

  1. capable of flowing and easily changing shape

  2. of, concerned with, or using a fluid or fluids

  1. constantly changing or apt to change

  2. smooth in shape or movement; flowing

Origin of fluid

C15: from Latin fluidus, from fluere to flow

Derived forms of fluid

  • fluidal, adjective
  • fluidness, noun
  • fluidly or fluidally, adverb

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for fluid


[ flōōĭd ]

  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. See also state of matter viscosity.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for fluid


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

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.