Bitter ender (4)
I believe the answer is:
ness
'bitter ender' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ness that I've seen before include "Famous loch" , "Headland, cape" , "Loch in the Great Glen" , "Scottish Lough containing legendary monster" , "Where you're reputed to see monster" .)