Scottish body of water (4)
'scottish body of water' 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" , "Body of (Scottish?) water" , "Ness or Lomond, for instance" , "Scottish word for lake" .)
(Other definitions for loch ness that I've seen before include "Great Glen water" , "Scottish lake with mysterious monster" , "where monster lurks?" , "Scottish water stretch with alleged monster" , "Scene of monsters?" .)