The joint in the middle of your arm where it bends, between the shoulder and the wrist.
From Old English 'elnboga', a compound of 'eln' (forearm) and 'boga' (bend, bow). The word has long described both the body part and things shaped like its angle.
The same bend that lets you touch your own shoulder inspired 'elbow room'—the space you need to move freely. Pipes, roads, and rivers with sharp turns are still described as having 'elbows' because of this shape match.
Complete word intelligence in one call. Free tier — 50 lookups/day.