Apprentice not starting profitable activity (6)
I believe the answer is:
earner
'profitable activity' is the definition.
'apprentice not starting' is the wordplay.
'apprentice' becomes 'learner' (synonyms).
'not starting' means to remove the first letter.
'learner' with its initial letter taken off is 'EARNER'.
(Other definitions for earner that I've seen before include "Something bringing in money" , "Cash job" , "Someone, or something, that provides income" , "One receives wages in return for labour" , "The one who brings home the money" .)