Unfit

wiktionary

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From un- +‎ fit.

etymonline

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unfit (adj.)

1540s, "not suitable" (in reference to things), from un- (1) "not" + fit (adj.). Related: Unfitness. In reference to persons or human qualities, attested from 1550s.

unfit (v.)

"to render unfit," 1610s, from unfit (adj.), or else from un- (2) "reverse of" + fit (v.). Related: Unfitted; unfitting.