Relating to or resembling the adenoids, the lymphoid tissue at the back of the nose and throat that helps fight infection.
From Greek 'aden' (gland) + '-oid' (resembling), with the adjective suffix '-al'. The adenoids themselves were named because they resemble small glands, though they're actually lymphoid tissue.
When someone talks about an 'adenoidal voice,' they're describing that nasal-sounding speech that happens when enlarged adenoids block airflow—this is one of those medical terms that actually made its way into everyday language.
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