Bishop on brink at border (4)
I believe the answer is:
brim
'border' is the definition.
(I've seen this in another clue)
'bishop on brink' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'on' means one lot of letters go next to another.
'brink' becomes 'rim' (I've seen this in another clue).
'b'+'rim'='BRIM'
'at' acts as a link.
(Other definitions for brim that I've seen before include "Lip of bowl, cup etc" , "Lip; part of a hat" , "Cup's lip" , "Top edge of a container" , "Lip; part of 6 Down" .)