clavicle (n.)

"collarbone," 1610s, from Middle French clavicule "collarbone" (16c.), also "small key," from Medieval Latin clavicula "collarbone" (used c. 980 in a translation of Avicenna), special use of classical Latin clavicula, literally "small key, bolt," diminutive of clavis "key" (from PIE root *klau- "hook"); in the anatomical sense a loan-translation of Greek kleis "key, collarbone," which is from the same PIE source. So called supposedly from its function as the "fastener" of the shoulder. Related: Clavicular.