a. (sb.) Anat. [f. Gr. κλείς, κλειδ- key, clavicle + MASTOID.] Pertaining to the clavicle and mastoid process; applied to the posterior part of the sterno-cleido-mastoid muscle.
1847–9. Todd, Cycl. Anat., IV. 725/1. That part … becomes confounded with the deltoid and with the cleido-mastoid.
1882. in Syd. Soc. Lex.
