A pound for a priest’s vestment (3)
I believe the answer is:
alb
'priest's vestment' is the definition.
(I've seen this before)
'a pound for a' is the wordplay.
'a pound' becomes 'lb' ('lb' can be a synonym of 'pound').
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'lb' put after 'a' is 'ALB'.
(Other definitions for alb that I've seen before include "Priest's long white sleeved vestment" , "Cover" , "Clerical vestment." , "Devotional vestment" , "Long white robe worn by proest" .)