- fit (n.1)
- 1823, "the fitting of one thing to another," later (1831) "the way something fits." Origin obscure, possibly from O.E. fitt "a conflict, a struggle" (see fit (n.2)).
- fit (n.2)
- "paroxysm, sudden attack" (as of anger), 1547, probably via M.E. sense of "painful, exciting experience," from O.E. fitt "conflict, struggle," of uncertain origin, with no clear cognates outside Eng. Phrase by fits and starts first attested 1620. Fitful was used once by Shakespeare ("Macbeth" iii.2) in sense of "characterized by fits," then revived by Scott (1810) with a sense of "shifting, changing."
- fit (adj.)
- "suited to the circumstances, proper," c.1440, of unknown origin, perhaps from M.E. noun fit "an adversary of equal power" (c.1250), which is perhaps connected to fit (n.1). The verb meaning "to be the right shape" is first attested 1581. First record of fitness is from 1580. Survival of the fittest (1867) coined by H. Spencer.