Entry 3 senses · 2 variants Webster, 1913 Adenoid /ăd'-ən-oidˌ/ · Ad·e·noid · IPA /ˈæd.əˌnɔɪd/ a. n. 01 a. Glandlike; glandular. 1. Glandlike; glandular. 02 n. A swelling produced by overgrowth of adenoid tissue; -- usually in pl. 1. A swelling produced by overgrowth of adenoid tissue; -- usually in pl.(Med.) 2. Lymphoid tissue in the roof of the nasopharynx; -- often in the pl.(Med.)