Crossword Genius

Cousin of a firth

Ross

I believe the answer is:

loch

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

I've seen this clue in The New York Times.
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