Clan
From the Gaelic “clann,” which means literally “children”
Mac-
From the Gaelic “mac,” meaning “son”
O’
From the Gaelic “Ó,” meaning “grandson”, “grandchild” or “descendant”; “Ní” is the femine form of Ó, 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.
Documentation:
Ulster Ancestry. 24 December 2012
http://www.UlsterAncestry.com/Irish-names/