Maybe rat's lair beset by decay (6)

I believe the answer is:

rodent

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'maybe rat's' is the definition.
I can't tell whether this defines the answer.

'lair beset by decay' is the wordplay.
'lair' becomes 'den' (synonyms).
'beset by' is an insertion indicator ('beset' could historically mean 'cover').
'decay' becomes 'rot' (rot can mean to decay).
'den' put inside 'rot' is 'RODENT'.

Can you help me to learn more?

(Other definitions for rodent that I've seen before include "Vermin" , "Nibbler" , "Mouse or squirrel, say" , "Eg, mouse, squirrel" , "Eg, mouse or rat" .)

I've seen this clue in The Guardian.

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