Crossword Genius

Piece of brass returned to border (4)

Ross

I believe the answer is:

abut

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'to border' is the definition.
('abut' can be a synonym of 'border')

I cannot understand how the rest of the clue works.

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(Other definitions for abut that I've seen before include "Meet" , "Join" , "Neighbour" , "Be next door to" , "Lie adjacent to" .)

I've seen this clue in The Daily Express.
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