Meaning

noun a collection of lymphatic tissue in the throat behind the uvula (on the posterior wall and roof of the nasopharynx)

adjective relating to or resembling lymphatic glands or lymphoid tissue

originLate 19th century borrowing from French adénoïde, from New Latin adenoīdēs, from Ancient Greek ᾰ̓δενοειδής (ădenoeidḗs, “glandular”), from ᾰ̓δήν (ădḗn, “gland”) + -ο- (-o-) + -ειδής (-eidḗs, “-oid, -like”); equivalent to aden- + -oid. The noun is derived from ellipsis of tumeur adénoïde (“glandular tumor”).

Etymology from Wiktionary, CC BY-SA 3.0