This is an anglicisation of MacDonald that  has been in use in Scotland, particularly Edinburgh, from the fourteenth century.  In Ulster it is most common in Co. Antrim and to a lesser extent Co. Armagh.

Fairly early on the clan name of the great MacDonalds, Lords of the Isles, began to be spelt in a variety of ways, including Donaldson, Donillson and Donnelson, forms recorded in old charters of the MacDonnells of Antrim (from whom the present Earl of Antrim descends).  In the 'census' of 1659 Donnellson appears as a 'principal name' in Co. Antrim (see Connell, MacDonald and MacDonnell).

Around 1900 Donaldson was being used interchangeably with Donnelly (see Donnelly) in parts of the Coleraine district of Co. Derry.



Clan From the Gaelic clann which means literally 'children'.
Mac- From the Gaelic mac, meaning 'son'
O' From the Gaelic , meaning 'grandson', 'grandchild' or 'descendant'; N is the femine form of , meaning 'daughter' or 'descendant'
Plantation (Ulster) The redistribution of escheated lands after the defeat of the Ulster Gaelic lords and the 'Flight of the Earls' in 1607.  Only counties Donegal, Derry, Tyrone, Armagh, Fermanagh and Cavan were actually 'planted', portions of land there being distributed to English and Scottish families on their lands and for the building of bawns.
Sept A family group of shared ancestry living in the same locality
Undertakers Powerful English or Scottish landowners who undertook the plantation of British settlers on the lands they were granted.
Gaelic This word in Ireland has no relation to Scotland.  As a noun it is used to denote the Irish language, as an adjective to denote native Irish as opposed to Norman or English origin.
Erenagh From the Irish Gaelic airchinneach, meaning 'hereditary steward of church lands'.  A family would hold the ecclesiastical office and the right to the church or monastery lands, the incumbent at any one time being the erenagh.