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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") + -eides "form, shape" (see -oid). The noun, short for thyroid gland, is recorded from 1849.
thyroid thy·roid (thī'roid')
The thyroid gland.
The thyroid cartilage.
A powdered preparation of the thyroid gland of certain domestic animals, used in the treatment of cretinism and myxedema, in certain cases of obesity, and in skin disorders.