Set up trap in aforementioned puzzles (7)
I believe the answer is:
enigmas
'puzzles' is the definition.
(I've seen this before)
'set up trap in aforementioned' is the wordplay.
'set up' shows that the letters should be reversed in order.
'trap' becomes 'gin' (I've seen this before).
'in' means one lot of letters goes inside another.
'aforementioned' becomes 'same' ('same' can be similar in meaning to 'aforementioned').
'gin' inserted into 'same' is 'samgine'.
'samgine' back-to-front is 'ENIGMAS'.
(Other definitions for enigmas that I've seen before include "'Mysteries, riddles (7)'" , "Puzzles - mysteries" , "Problems" , "'Puzzles, riddles (7)'" , "They're mysterious or difficult to understand" .)