hip

Hip comes from Middle English hipe or hupe, from Old English hype, from Proto-Germanic *hupiz, tracing back to a Proto-Indo-European root *ḱewb-, itself from *ḱew- meaning 'to bend.' Related forms across old languages point to the same idea of a curve or hollow — the Ancient Greek kúbos even meant 'hollow in the hips.'

The body-part sense stayed fairly stable from Old English onward, always naming that bending joint. A separate slang sense, 'drug addict,' arose because opium users would lie on their hips while smoking — a much later and unrelated development.

The facts note that hip shares its deep root with the word high, both tracing back through the same Germanic and Indo-European lineage.