Thȳ'roid, a.

a. [Fr. thyroïde, Gr. θυρεοειδής, shield-shaped, from θυρεός, a large, oblong shield, from θύρα, a door, and εἶδος, form.] Resembling a shield.

Thyroid cartilage (Anat.), a cartilage constituting the anterior, superior, and largest part of the larynx, and sometimes popularly called Adam's apple. Hooper.— Thyroid gland, a firm vascular substance, of a reddish-yellow color, situated on the sides and front of the upper part of the trachea. It is copiously supplied with blood, but has no excretory duct, and is not therefore, properly speaking, a gland. Its function is not known; but Sir Charles Bell supposes that it is designed to prevent the vibrations of sound originating in the larynx from being propagated downward. It is the seat of the bronchocele, or goiter.