c. 1200, "fighting equipment, armor and weapons," probably from Old Norse gørvi (plural gørvar) "apparel, gear," related to görr, gørr, gerr "skilled, accomplished; ready, willing," and to gøra, gørva "to make, construct, build; set in order, prepare," a very frequent verb in Old Norse, used in a wide range of situations from writing a book to dressing meat. This is from Proto-Germanic *garwjan "to make, prepare, equip" (source also of Old English gearwe "clothing, equipment, ornament," which may be the source of some uses; Old Saxon garwei; Dutch gaar "done, dressed;" Old High German garo "ready, prepared, complete," garawi "clothing, dress," garawen "to make ready;" German gerben "to tan").
From early 14c. as "wearing apparel, clothes, dress;" also "harness of a draught animal; equipment of a riding horse." From late 14c. as "equipment generally; tools, utensils," especially the necessary equipment for a certain activity, as the rigging of a sailing ship. Meaning "toothed wheel in machinery" first attested 1520s; specific mechanical sense of "parts by which a motor communicates motion" is from 1814; specifically of a vehicle (bicycle, automobile, etc.) by 1888. Slang for "male sex organs" from 1670s.