Calf is native and old: Old English cealf, from a Germanic word for the young of a cow, with relatives in German Kalb, Old Norse kalfr and Gothic kalbo. The underlying root seems to have meant "to swell," giving words for womb, foetus and the young of an animal — the swelling and what comes out of it.
Calf is the native half of one of English's animal-and-meat pairs; the French word for the meat is veal. What is unusual is that English has a second, apparently unrelated calf — the fleshy back of the lower leg — which came from Old Norse kalfi in the early 1300s and may or may not descend from the same Germanic root. The uses that grew off the animal are all later and all about size or material: calf leather from 1727, the young of marine mammals from 1725, and icebergs breaking off glaciers from 1818.
calf (n.1) "young of a bovine animal," Old English cealf (Anglian cælf ) "young cow," from Proto-Germanic *kalbam (source also of 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." The elliptical sense of "fine kind of leather made from the skin of a calf" is from 1727 (short for calf-skin , 1580s). It was extended by 1725 to the young of marine mammals, the adults of which are called bulls and cows. It has been used of icebergs that break off from glaciers from 1818 (perhaps from Scandinavian uses in reference to a small islet lying near a large one). Finnish kalpe is from Germanic. Golden calf "idol" is from Exodus. calf (n.2) "thick, fleshy part of the back of the lower human leg," early 14c., from Old Norse kalfi , a word of unknown origin; possibly from the same Germanic root as calf (n.1). It is relatively larger in man than in other mammals for the support of the body standing upright. Of garments, calf-length is from 1956. also from early 14c.