elbow (n.) Look up elbow at Dictionary.com
c.1200, elbowe, from Old English elnboga, from ell "length of the forearm" + boga "bow, arch," from West Germanic *alinobogan, from Proto-Germanic *elino-bugon, literally "bend of the forearm" (cf. Middle Dutch ellenboghe, Dutch elleboog, Old High German elinbogo, German Ellenbogen, Old Norse ölnbogi).

Second element related to Old English bugan "to bend" (see bow (v.)); first element from *alina "arm," from PIE *el- (1) "elbow, forearm" (see ell (n.1)). Phrase elbow grease "hard rubbing" is attested from 1670s, from jocular sense of "the best substance for polishing furniture." Elbow room attested from mid-16c.
elbow (v.) Look up elbow at Dictionary.com
"thrust with the elbow," c.1600, from elbow (n.). Figurative sense is from 1863. Related: Elbowed; elbowing.