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c.1300, "come to life; give life to," from quick (adj.) + -en (1). Meaning "become faster" is from 1805. Related: Quickened; quickening. An earlier verb was simply quick (c.1200), from Old English gecwician.
quicken quick·en (kwĭk'ən)v. quick·ened, quick·en·ing, quick·ens
To become more rapid.
To reach the stage of pregnancy when the fetus can be felt to move.