Hi Jaki,
It would appear that it was the name of a house and it is still marked on the maps today. It is near St. Mary's on Mainland, Orkney. I have found it on some old maps as well, marked Clett.
Go to
http://www.old-maps.co.ukuse the gazetteer on the left hand side and navigate to Orkney, then St. Mary's. Click the left hand arrow at the side of the map twice and you should see Clett inside the pink rectangle marked, near the top. You can then use the buttons at the bottom to zoom in. You can also print the page off if you wish.
Now I just hope that I have identified it correctly! Find it on a modern map by using
http://www.streetmap.co.uk/and searching for it as a GB place.
Good luck.
Nell