Priest might trim one layer to make border (8)
I believe the answer is:
frontier
'border' is the definition.
(I know that border can be written as frontier)
'priest might trim one layer' is the wordplay.
'priest' becomes 'fr' (abbreviation as in a priest's title).
'might trim' becomes 'on' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'one layer' becomes 'tier' (tier is a kind of layer).
'fr'+'on'+'tier'='FRONTIER'
'to make' is the link.
Can you help me to learn more?
(Other definitions for frontier that I've seen before include "Wilderness at the edge of settled territory" , "Border (not yet crossed?)" , "Border separating two countries" , "wild area" , "Limit" .)