From Old English 'cin' and PIE *genu- (chin, jaw) — may be related to 'knee' through a shared concept of 'angle.'
The protruding part of the face below the mouth, formed by the apex of the lower jaw.
From Old English 'cin, cinn' (chin), from Proto-Germanic *kinnuz (chin), from PIE *ǵénu- (chin, jawbone). This root has extraordinary continuity across Indo-European: Latin 'gena' (cheek), Greek γένυς (génus, jaw, chin), Sanskrit हनु (hánu, jaw), Tocharian A 'śanweṃ' (jaws), Armenian ծնօտ (cnot, jaw), Old Irish 'gin' (mouth), and Gothic 'kinnus' (cheek). The semantic variation is revealing — the same PIE root designates the chin in Germanic, the cheek in Latin, the jaw in Greek and Sanskrit, and the mouth in Celtic. This suggests the original PIE word referred broadly to the lower face
'Chin,' 'knee,' and 'genuflect' may all be related at the deepest level. PIE *ǵenu- (chin/jaw) and *ǵónu (knee) are so similar that many linguists believe they share a common ancestor meaning 'angle' or 'joint.' Both the jaw and the knee are angular joints — the chin is where the jaw bends, the knee is where the leg bends. German 'Kinn' (chin) and 'Knie' (knee) show the same pattern.