Thyroid

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early 18th century (as an adjective): from Greek (khondros) thureoeidēs ‘shield-shaped (cartilage)’, from thureos ‘oblong shield’.

wiktionary

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Borrowed from New Latin thyreoīdēs, from Ancient Greek θῠρεοειδής(thureoeidḗs, “shield-shaped”), from θῠρεός(thureós, “oblong shield”) +‎ -ειδής(-eidḗs, “-form, -like”).

etymonline

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thyroid (adj.)

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 root *dhwer- "door, doorway") + -eides "form, shape" (see -oid). The noun, short for thyroid gland, is recorded from 1849.