Endeavour to slash regular outlay for clothing (7)
I believe the answer is:
raiment
'for clothing' is the definition.
(raiment is a kind of clothing)
'endeavour to slash regular outlay' is the wordplay.
'endeavour' becomes 'aim' (aim can mean to endeavour or try).
'to slash' indicates putting letters inside (inserted letters slash into the word).
'regular outlay' becomes 'rent' (rent is a regular payment).
'aim' placed into 'rent' is 'RAIMENT'.
(Other definitions for raiment that I've seen before include "Clothing (archaic)" , "Tire man (anag.)" , "Garb" , "Something put on" , "investment" .)