Right to retain the last word about one’s clothing (7)
I believe the answer is:
raiment
'clothing' is the definition.
(I know that raiment is a type of clothing)
'right to retain the last word about one's' is the wordplay.
'right' becomes 'rt' (abbreviation as in Rt Hon- the Right Honourable).
'to retain' means one lot of letters goes inside another.
'the last word' becomes 'amen' (last word in a prayer).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'rt' placed around 'amen' is 'rament'.
'rament' placed around 'i' is 'RAIMENT'.
(Other definitions for raiment that I've seen before include "Especially fine or decorative clothing" , "Clobber" , "Wear" , "Something put on" , "Garment" .)