1987 Costner role (4)
I believe the answer is:
ness
'1987 costner role' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ness that I've seen before include "Scottish lake with traditional monster" , "Loch in the Great Glen" , "head" , "Loch of monster fame" , "Scottish loch - headland" .)