Erse (early Scots for "Irish") Can be used as an adjective, but is more often used as a noun referring to the Irish language. Originally it could be used in reference to both things Irish and Highlander (in the Gaidhealtachd sense), but latterly it specifically refers to Irish. The term is now archaic, and in most contexts is considered derogatory.
It has been used in Scotland to underline the (supposed) foreignness of (Scottish) Gaelic (Gàidhlig). The word Gaelic (normally meaning Scots Gaelic) has been used by opponents of Irish language (Gaeilge) revival in Ireland in a similar way.
