The Norse–Gaels were a people who dominated much of the Irish Sea region, including the Isle of Man and western Scotland for a part of the Middle Ages; they were of Gaelic and North Germanic origin and as a whole exhibited a great deal of Gaelic and Norse cultural syncretism. Other modern terms used include Scoto-Norse, Hiberno-Norse, Irish–Norse and Foreign Gaels.
The correct translation for Gall-Ghàidheil or any of the variant spellings is “Foreign Gaels” and is not specifically used to refer to Norse foreigners. It is a general term to describe a particular ethnic grouping of foreigners of which the Norse formed part. This term is subject to a large range of variations depending on chronological and geographical differences in the Gaelic language, i.e., Gall Gaidel, Gall Gaidhel, Gall Gaidheal, Gall Gaedil, Gall Gaedhil, Gall Gaedhel, Gall Goidel, etc. The modern term in Irish is Gall-Ghaeil, while the Scottish Gaelic is Gall-Ghàidheil.
The people concerned often called themselves ‘Ostmen’ or ‘Austmenn’ (East-men), a name preserved in a corrupted form in the Dublin area known as Oxmantown which is derived from ‘Austmanna-tún’ (Homestead of the Eastmen). In contrast, they called the Irish ‘Vestmenn’ (West-men).
The Norse–Gaels originated in Viking colonies of Ireland and Scotland, whose inhabitants became subject to the process of Gaelicisation. As early as the ninth century, most colonists (except the Norse who settled in Cumbria) intermarried with native Gaels and adopted the Gaelic language as well as many Gaelic customs. Many left their original worship of Norse gods and converted to Christianity, and this contributed to the Gaelicisation.
Gaelicised Scandinavians dominated region of the Irish Sea until the Norman era of the twelfth century. They founded long-lasting kingdoms, such as the Kingdoms of Man, Argyll, Dublin and Galloway, as well as taking control of the Norse colony at York.
The Lords of the Isles, whose sway lasted until the sixteenth century, as well as many other Gaelic rulers of Scotland and Ireland, traced their descent from Norse–Gaels’ settlements in North West Scotland concentrated mostly in the Hebrides.
A class of mercenaries now known as “gallowglass” – a term evolving from the Irish for “foreign soldier” – served as warriors for Irish kings from the early 13th century until the middle of the 16th century, many settling in Ireland at the completion of their service.
The Hebrides islands in Scotland are to this day known in Gaelic as Innse Gall, the islands of foreigners.
Today, many surnames particularly connected with Gaeldom are of Norse origin, especially in the Hebrides and Isle of Man.
(source: http://bit.ly/12is934, photograph http://bit.ly/1LZCdYw)