Fluid, a.
Etymology: [L. fluidus, fr. fluere to flow: cf. F. fluide. See Fluent.]
Having particles which easily move and change their relative position without a separation of the mass, and which easily yield to pressure; capable of flowing; liquid or gaseous.
1 other Webster entry under this spelling
Fluid, n.
A fluid substance; a body whose particles move easily among themselves.
Note: Fluid is a generic term, including liquids and gases as species. Water, air, and steam are fluids. By analogy, the term is sometimes applied to electricity and magnetism, as in phrases electric fluid, magnetic fluid, though not strictly appropriate. Fluid dram, or Fluid drachm, a measure of capacity equal to one eighth of a fluid ounce. -- Fluid ounce. (a) In the United States, a measure of capacity, in apothecaries' or wine measure, equal to one sixteenth of a pint or 29.57 cubic centimeters. This, for water, is about 1.04158 ounces avoirdupois, or 455.6 grains. (b) In England, a measure of capacity equal to the twentieth part of an imperial pint. For water, this is the weight of the avoirdupois ounce, or 437.5 grains. -- Fluids of the body. (Physiol.) The circulating blood and lymph, the chyle, the gastric, pancreatic, and intestinal juices, the saliva, bile, urine, aqueous humor, and muscle serum are the more important fluids of the body. The tissues themselves contain a large amount of combined water, so much, that an entire human body dried in vacuo with a very moderate degree of heat gives about 66 per cent of water. -- Burning fluid, Elastic fluid, Electric fluid, Magnetic fluid, etc. See under Burning, Elastic, etc.
Shades of meaning
A fluid is a substance that, like air or water, yields to any force that tends to change its form; a liquid is a body in that 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, tho 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.