-séin
Definitions (by source)
demonstrative enclitic that; eiséin 621, doséin 1908, aindséin 2828.
Duanaire Mhéig Uidhir: The poembook of Cú Chonnacht Mág Uidhir, Lord of Fermanagh 1566-1589. Editor: David Greene. Translator: David Greene.
only in ainn-séin, ‘then,’ ‘there,’ not distinct in meaning from ann sin’ [séin, earlier sidhéin, a blend of O. Ir. –side, ‘the latter,’ and féin, is enclitic, and palatalises prec. cons.]
Trí Bior-Ghaoithe an Bháis: The Three Shafts of Death. Editor: Osborn Bergin.