Word Origin & History
O.E. lim "limb, joint, main branch of a tree," from P.Gmc. *limu- (cf. O.N. limr "limb," lim "small branch of a tree"), a variant of *liþu- (cf. O.E. liþ, O.Fris. lith, O.N. liðr, Goth. liþus "a limb;" with prefix ga-, source of Ger. glied "limb, member"), from PIE base *lei- "to
bend, be movable, be nimble." The parasitic -b began to appear late 1500s for no reason. In O.E., M.E., and until lately in dial., it could mean "any visible body part."
"The lymmes of generacion were shewed manyfestly." [Caxton, "The subtyl historyes and fables of Esope, Auyan, Alfonce, and Poge," 1484]
Hence, limb-lifter "fornicator" (1570s). To go out on a limb in figurative sense is from 1897. Life and limb in ref. to the body inclusively is from c.1200.
1590s, "edge of a quadrant or other instrument," from L. limbus "border, hem, fringe, edge," cognate with Skt. lambate "hangs down," English limp
. Astronomical sense of "edge of the disk of a heavenly body" first attested 1670s.