gear (n.) Look up gear at Dictionary.com
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 *garwian "to make, prepare, equip" (cognates: 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.
gear (v.) Look up gear at Dictionary.com
c.1200, "to equip oneself for fighting; to dress," probably from gear (n.) or from the verb in Old Norse. Mechanical meaning "put (machinery) in gear" is from 1851. Related: Geared; gearing.
gear (adj.) Look up gear at Dictionary.com
"stylish, excellent," British slang, 1951 (popularized c.1963 by the Beatles), said to be from earlier that's the gear, an expression of approval (1925), from gear (n.).