A pound for vestment (3)
I believe the answer is:
alb
'vestment' is the definition.
(alb is a kind of vestment)
'a pound' is the wordplay.
'pound' becomes 'lb' ('lb' can be a synonym of 'pound').
'a'+'lb'='ALB'
'for' acts as a link.
(Other definitions for alb that I've seen before include "Cover" , "clerical belongings" , "Priests robe made in Balbriggan" , "Without hindrance" , "Long white robe worn by Christian priest" .)