A singer engaged in criminal activity (2,2)
I believe the answer is:
at it
'engaged in criminal activity' is the definition.
'at it' can be an answer for 'engaged' (I've seen this in another clue). I am unsure of the 'in criminal activity' bit.
'a singer' is the wordplay.
'singer' becomes 'tit' (type of songbird).
'a'+'tit'='AT IT'
Can you help me to learn more?
(Other definitions for at it that I've seen before include "working hard" , "Occupied (in crime?)" , "Up to no good" , "occupied in a particular way" , "Engaged in something particular" .)