fleshy part of the lower leg, early 14c., from Old Norse kalfi, source unknown; possibly from the same Germanic root as calf (n.1).
"young cow," Old English cealf (Anglian cælf) "young cow," from West Germanic *kalbam (cf. Middle Dutch calf, Old Norse kalfr, German Kalb, Gothic kalbo), perhaps from PIE *gelb(h)-, from root *gel- "to swell," hence, "womb, fetus, young of an animal." Elliptical sense of "leather made from the skin of a calf" is from 1727. Used of icebergs that break off from glaciers from 1818.
Prepare for a joyful occasion or a warm welcome. For example, When Bill comes home from his trip to Korea we're going to kill the fatted calf. This expression alludes to the parable of the prodigal son (Luke 15:11–32), whose father welcomed him by serving the choicest calf after his return. [Early 1600s]