whirl-bone

The story

1. Old English · inherited fromhweorfbān“a joint, kneecap, vertebra”
2. Middle English · inherited fromwhirlebon
3. English todaywhirl-bone

From Middle English whirlebon, whyrlebone, whorlbane (“hip or hip joint; the thighbone, femur; the rounded head of the femur; the kneecap, patella; a vertebra; ankle”), perhaps an alteration of Old English hweorfbān (“a joint, kneecap, vertebra”), equivalent to whirl + bone. Cognate with Scots whorlebone, whorle-bane (“hip bone, joint, vertebra”), German Wirbelbein (“vertebra”).