1690s (in reference to both the cartilage and the gland), from Greek thyreoiedes "shield-shaped" (in khondros thyreoiedes "shield-shaped cartilage," used by Galen to describe the "Adam's apple" in the throat), from thyreos "oblong, door-shaped shield" (from thyra "door," from PIE *dhwer-; see door) + -eides "form, shape" (see -oid). The noun, short for thyroid gland, is recorded from 1849.