Famous loch (4)
I believe the answer is:
ness
'famous loch' 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 "head" , "Famous loch" , "Scottish Lough containing legendary monster" , "Scottish Loch famed for monster" , "Scottish Loch with legendary monster" .)