Crossword Genius

Insensitive, a singer working intensely (4,2,2)

Ross

I believe the answer is:

hard at it

'working intensely' is the definition.

'insensitive a singer' is the wordplay.
'insensitive' becomes 'hard' (associated in meaning).
'singer' becomes 'tit' (type of songbird).
'hard'+'a'+'tit'='HARD AT IT'

(Other definitions for hard at it that I've seen before include "Working very busily" , "Very busy - that raid (anag)" , "Really busy" .)

I've seen this clue in The Guardian.
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