cleido-

combining form, with -o-, from Greek kleid-, kleís (earlier Attic klēis, Epic & Ionic klēḯs, Doric klaik-, kláix) "bar, bolt (of a door), catch or hook used to move the bolt from the outside, key, collarbone," going back to Attic & Ionic *klēwī-d-, Doric *klāwī-k-, going back to Indo-European *kleh₂u-iH-, from a base *kleh₂u- "nail, peg, key," whence probably also Latin clāvis "key," clāvus "nail, rivet"