Monster's loch (4)
I believe the answer is:
ness
'monster's 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 "Scottish Loch with legendary monster" , "Scottish lake with traditional monster" , "Loch of monster fame" , "Scottish Lough containing legendary monster" , "Where you're reputed to see monster" .)