Glandular decay in mercenary (7)

I believe the answer is:

parotid

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'glandular' is the definition.
Both the answer and definition are adjectives.
Perhaps you can see an association between them that I don't see?

'decay in mercenary' is the wordplay.
'decay' becomes 'rot' (rot can mean to decay).
'in' indicates putting letters inside.
'mercenary' becomes 'paid' (similar in meaning).
'rot' inserted into 'paid' is 'PAROTID'.

Can you help me to learn more?

(Another definition for parotid that I've seen is " Sort of duct".)

I've seen this clue in The Times.

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