Times when naturism retreat rejected trousers (5)
I believe the answer is:
terms
'times' is the definition.
(I've seen this before)
'naturism retreat rejected trousers' is the wordplay.
'trousers' says the answer is hidden in the clue (trouser can mean to steal or take).
'rejected' shows that the letters should be reversed in order.
'smret' is hidden in the letters of 'naturism retreat'.
'smret' written backwards gives 'TERMS'.
'when' acts as a link.
(Other definitions for terms that I've seen before include "Conditions; charge" , "Spells" , "qualifications" , "words" , "Conditions; fee" .)