Old English twinclian "to twinkle, wink," frequentative of twincan "to wink, blink," with -el (3). Twincan is related to Middle High German zwinken, German zwinkern, and probably somehow imitative. Related: Twinkled; twinkling. The noun is recorded from 1540s. Phrase in the twinkling of an eye "in a very brief time" is attested from c. 1300.