Crossword Genius

On the phone, mention also experiencing irritation of the glands (7)

Ross

I believe the answer is:

adenoid

I'm a little stuck... Click here to teach me more about this clue!

'on' is the definition.
Although both the answer and definition are adjectives, I cannot see how they can define each other.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for adenoid that I've seen before include "Gland-like - I add one (anag)" , "Glandular" .)

I've seen this clue in The Independent.
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