Old English sceap, scep, from West Germanic *skæpan (cf. Old Saxon scap, Old Frisian skep, Middle Low German schap, Middle Dutch scaep, Dutch schaap, Old High German scaf, German Schaf), of unknown origin. Not found in Scandinavian or Gothic, and with no known cognates outside Germanic. The more usual Indo-European word for the animal is represented by ewe.
As a type of timidity, from Old English; the meaning "stupid, timid person" is attested from 1540s. The image of the wolf in sheep's clothing was in Old English (from Matt. vii:15); that of separating the sheep from the goats is from Matt. xxv:33. To count sheep in a bid to induce sleep is recorded from 1854. Sheep's eyes "loving looks" is attested from 1520s (cf. West Frisian skiepseach, Dutch schaapsoog, German Schafsauge).