An Etymological Dictionary of the German Language/Annotated/Busen
Busen, masculine, ‘bosom,’ from the equivalent Middle High German buosen, buosem, Old High German buosam, buosum, masculine.; compare Old Saxon bôsm, Dutch boezem, Anglo-Saxon bôsm, English bosom; in East-Teutonic (Gothic, Scandinavian) the corresponding word (Gothic *bôsma-) is wanting. It may perhaps be allied to Bug, Middle High German buoc, ‘arm, shoulder’ (pre-Teutonic bhâghu-); but since a pre-Teutonic bhâghsmo, bhâksmo- does not occur in the cognate languages, nothing can be cited in favour of that explanation; at all events, Busen is not allied to biegen.