Word Origin & History
arm"body part," O.E. earm "arm," from P.Gmc. *armaz (cf. O.S., M.Du., Ger. arm, O.N. armr, O.Fris. erm), from PIE base *ar- "fit, join" (cf. Skt. irmah "arm," Armenian armukn "elbow," O.Prus. irmo "arm," Gk. arthron "a joint," L. armus "shoulder"). Arm of the sea was in O.E. Arm-twister "powerful persuader"
is from 1938. Arm-wrestling is from 1971.
"They wenten arme in arme yfere Into the gardyn" [Chaucer]
arm"weapon," c.1300, from O.Fr. armes (pl.), 11c., from L. arma "weapons," lit. "tools, implements (of war)," from PIE base *ar- "fit, join." The notion seems to be "that which is fitted together." Meaning "heraldic insignia" (in coat of arms, etc.) is early 14c.; originally they were borne on shields of
fully armed knights or barons. The verb meaning "to furnish with weapons" is from c.1200.