Lomond or Ness (4)
I believe the answer is:
loch
'lomond or ness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for loch that I've seen before include "Scots lake" , "Eg, Ness" , "Scottish word for lake" , "Body of (Scottish?) water" , "A Scottish lake like Lomond" .)