fluid (adj.)

early 15c., "liquid, capable of flowing," from Middle French fluide (14c.) and directly from Latin fluidus "fluid, flowing, moist," from fluere "to flow" (see fluent). Figurative use, of non-material things, "not fixed or rigid," from 1640s. Related: Fluidly.

fluid (n.)

"substance capable of flowing," 1660s, from fluid (adj.). Related: Fluidal (1869), fluidic (1821, Marmaduke Tulket).

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