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fluid

nounadjectivecommon in dialogue

  • United Kingdom//ˈfluːɪd//
  • United Kingdom//ˈflʉwɪd//
  • United States//ˈflu.ɪd//
  • Australia//ˈflʉːɪd//
  • Scotland//ˈflʉ.ɪd//

Any substance which can flow with relative ease, tends to assume the shape of its container, and obeys Bernoulli's principle; a liquid, gas or plasma.

noun

  1. 1

    Any substance which can flow with relative ease, tends to assume the shape of its container, and obeys Bernoulli's principle; a liquid, gas or plasma.

    An extreme version of vorticity is a vortex. The vortex is a spinning, cyclonic mass of fluid, which can be observed in the rotation of water going down a drain, as well as in smoke rings, tornados and hurricanes.

  2. 2

    A liquid (as opposed to a solid or gas).

    fluid inclusion Petrology, a tiny fluid- or gas-filled cavity in an igneous rock. 1-100 micrometers in diameter, formed by the entrapment of a fluid, typically that from which the rock crystallized.

    The Doctor: Get a good night's sleep and drink plenty of fluids. / Kes: Fluids? / The Doctor: Everybody should drink plenty of fluids.

    For studying interfaces between solid and another solid, fluid, or gas, a sample can be oriented with its reflecting surface(s) vertical (and with the scattering plane, as defined by nominal incident and reflected wavevectors, horizontal).

    Tenderness: is the lump tender? Composition: is the mass solid, fluid or gas?

  3. 3

    Intravenous fluids.

Etymology

Etymology tree Proto-Indo-European *bʰel-der. Proto-Indo-European *bʰlewH-der. Proto-Indo-European *bʰluH-yé-ti? Latin fluō Proto-Indo-European *dʰeh₁-der. Proto-Italic *-iðos Latin -idus Latin fluidusder. Middle English fluid English fluid From Middle English fluid, from Latin fluidus (“flowing; fluid”), from Latin fluō (“to flow”), from Proto-Indo-European *bʰleh₁- (“to swell; surge; overflow; run”). Akin to Ancient Greek φλύειν (phlúein, “to swell; overflow”). Not related to English flow, which is a native, inherited word from *plew-, but is distantly related from English bleat.

adjective

  1. 1

    Of or relating to fluid.

  2. 2

    In a state of flux; subject to change.

    Economics is a messy discipline: too fluid to be a science, too rigorous to be an art. Perhaps it is fitting that economists’ most-used metric, gross domestic product (GDP), is a tangle too. GDP measures the total value of output in an economic territory. Its apparent simplicity explains why it is scrutinised down to tenths of a percentage point every month.

  3. 3

    Moving smoothly, or giving the impression of a liquid in motion.

    Tom of the fluid pelvis, undulating about the living room in defiance of Michael's taboo on sensuality.

  4. 4

    Convertible into cash.

  5. 5

    rareGenderfluid.

    Oh, Loki made sure of that. My mortal parents blamed him for the way I was, for being fluid.

    As do renewals in genres such as romcoms and teen movies, which have updated sexist, heteronormative tropes to reflect audiences’ fluid, inclusive, queer realities.

Forms

plural
fluids
comparative
more fluid
superlative
most fluid
The neighbouring pagesAlphabetical order follows the rules of the language, not byte values: an accent decides only between two otherwise identical words, and Spanish files Ñ as a letter of its own.

Lexical content from Wiktionary, under CC BY-SA 4.0 · Source entry · Data version 2026-08-23

Rank among the words of the OpenSubtitles 2018 corpus — film and television subtitles, so spoken rather than written usage (CC BY-SA 3.0).