Definition of: fluid

(fl′id) adjective
Capable of flowing; liquid or gaseous.
—noun A substance that yields to any force tending to change its form; a liquid or gas. [<F fluide <L fluidus <fluere flow]
—flu·id′ic adjective
—flu·id′i·ty, flu′id·ness noun
—flu′id·ly adverb Synonyms (noun): gas, liquid. In comparison with the substance, fluid, a liquid is a body in a state in which the particles move freely among themselves, but remain in one mass, keeping the same volume, but taking always the form of the containing vessel; a liquid is an inelastic fluid; a gas is an elastic fluid that tends to expand to the utmost limits of the containing space. All liquids are fluids, but not all fluids are liquids; air and all the gases are fluids, but they are not liquids under ordinary circumstances, even if capable of being reduced to a liquid form by special means, as by cold and pressure. Water at the ordinary temperature is at once a fluid and a liquid. Antonym: solid.