Sources

Na Tathagan. “Fear nan Tathag”: Robertson

“Taag 1633; G. na Tathagan; Fear nan  Tathag, the goodman of Tagan. The singular nom. is thus Tathag, as in the 1633 spelling, a diminutive in form, which I take to be a loan from N. tađi, fem., an in-field, homefield. Tathag thus means the small in-field; na Tathagan, the small in-fields.” Watson 1904, 231

Na Tathagan: Wentorth, Faclan is Abairtean