Stylish clothing provided in catalogue (8)
I believe the answer is:
classify
'catalogue' is the definition.
(I know that catalogue is a kind of classify)
'stylish clothing provided' is the wordplay.
'stylish' becomes 'classy' (similar in meaning).
'clothing' is an insertion indicator (some letters cover up or clothe others).
'provided' becomes 'if' (eg 'provided it's sunny' means 'if it's sunny').
'classy' enclosing 'if' is 'CLASSIFY'.
'in' is the link.
(Other definitions for classify that I've seen before include "Make secret for security reasons" , "Arrange in divisions" , "Arrange in categories" , "Grade" , "Categorise or pigeonhole" .)