bone

Bone comes from Middle English bon, from Old English bān, from Proto-Germanic *bainą, itself from *bainaz meaning 'straight.' Some trace this further back to a Proto-Indo-European root meaning 'to hit, strike, beat.'

The word has stayed remarkably close to its original sense of a hard skeletal part throughout Old and Middle English into today's usage.

It's cognate with Dutch been and German Bein, both of which can mean either 'bone' or 'leg,' and with Old Norse beinn, meaning 'straight' or 'direct' — a sense that survives in English bain and Scots bein, meaning prompt or in good condition.