Crossword Genius

Keen to help a number trapped inside (4)

Ross

I believe the answer is:

avid

'keen' is the definition.
(thesaurus)

'help a number trapped inside' is the wordplay.
'help' becomes 'aid' ('aid' can be a synonym of 'help').
'a number' becomes 'v' (V is an example**).
'trapped inside' indicates putting letters inside.
'aid' placed around 'v' is 'AVID'.

'to' acts as a link.

(Other definitions for avid that I've seen before include "Greatly desirous" , "Fanatical" , "Keen or greedy" , "Greedy like diva" , "Burning" .)

I've seen this clue in the Evening Standard.
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