*bainaz

Of disputed origin. Likely from *bainą (‘bone, leg’) with the obvious semantic relationship. It seems unlikely that the reverse is true (*bainą < *bainaz), given that the term is only secure for North Proto-Germanic. (Urban 2015) makes a persuasive argument using cross-linguistic typological data to determine the dominant directionality of semantic change (bone > leg vs. leg > bone). He found that across the world's languages, there is a strong, recurrent metonymic pathway where words for ‘bone’ naturally shift to mean ‘leg’ or ‘limb’ (often via intermediate senses like ‘shinbone’ or ‘thighbone’). Conversely, languages very rarely take a broad word for ‘leg’ and narrow it down to mean ‘bone’.