Crossword Genius

Lake of Caledonian highlands primarily (4)

Ross

I believe the answer is:

loch

'lake' is the definition.
(loch is a kind of lake)

I don't understand how the remainder of the clue works.

(Other definitions for loch that I've seen before include "Ness or Lomond, for instance" , "A Scottish lake like Lomond" , "Scottish or Irish lake" , "Body of (Scottish?) water" , "A Scottish lake like Ness" .)

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