Sources

Dún Suibne: Glen Masain MS
oilen tsuibhne: Book of Clanranald [i.e. Eilean (an t-)Suibhne]
Caistel Tuinn: Robertson 2019, p. 342
Caisteal Suain: Watson in Dwelly
Caisteal Shuinn 1875 The Topography of Scotland The Gael, p. 56
Caisteal Shuinn: Dwelly [sourced from article above]
“Loch Sween and the old name Syffin is from old Suibhne” MacBain 356
Caisteal Suibhne: Watson 1926, 173
C[h]aistéal Suibhne: Book of the Dean of Lismore [Watson’s spelling]
Caisteal Suain / t-Suain / Suibhne / t-Suibhne: Nils Holmer notebooks

Loch Sween
loχ sʌiN’ə : Diack MS2276 [Loch Suinne or Suibhne]
Loch a’ Chaisteil: Robertson 2019, p. 342

Additional Information

There seem to be a number of competing traditions here.

Alternative Forms