Old English ban "bone, tusk," from Proto-Germanic *bainam (cognates: Old Frisian ben, Old Norse bein, Danish ben, German Bein). No cognates outside Germanic (the common PIE root is *os-; see osseous); the Norse, Dutch, and German cognates also mean "shank of the leg," and this is the main meaning in Modern German, but English never seems to have had this sense.

especially in bone up "study," 1880s student slang, probably from "Bohn's Classical Library," a popular series in higher education published by German-born English publisher Henry George Bohn (1796-1884) as part of a broad series of "libraries" he issued from 1846, totaling 766 volumes, continued after 1864 by G. Bell & Sons.