The Killers or Stock, Aitken and Waterman, say (6)
I believe the answer is:
hitmen
'the killers or stock aitken' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'and waterman say' is the wordplay.
I cannot really see how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
The remaining letters 'hitme' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for hitmen that I've seen is " Offers".)