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" (cognates: 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.