Brass covering northern hills (8)
I believe the answer is:
pennines
'hills' is the definition.
Both the answer and definition are plural nouns.
Perhaps there's a link between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for pennines that I've seen before include "Range of hills in England" , "chain of hills" , "English mountain range" , "Backbone of England" .)