An Etymological Dictionary of the German Language/Annotated/Bein
Bein, neuter, ‘bone, leg,’ from Middle High German bein, Old High German bein, neuter; compare Old Low German bén, Anglo-Saxon bân, English bone; Modern High German reserves the earlier meaning ‘bone’ still existing in Upper German in the words Beinhaus, Elfenbein, Fischbein, Falzbein, Gebein; the later signification, ‘lower part of the thigh,’ is recorded even in Old High German, Middle High German, and Old Icelandic. The Old Icelandic beinn, adjective, ‘straight,’ favours the supposition that originally at least the straight thigh-bones were termed Beine (bones). Gothic *bain, neuter, is by chance not recorded. A primitively Teutonic word with the primary meaning ‘bone,’ which cannot, however, be traced farther back (Latin os, Greek ὀστέον, Sanscrit asthi, asthan, to which an Aryan osth-, ‘bone,’ would correspond, are not represented, on the other hand, in the Teutonic group). Compare further Eisbein.