Lennon is primarily the anglicised form of the Irish O Leannain, from leannan, meaning "lover". However, O Leannain has also sometimes been anglicised as "Linnane" or even "Leonard". Additional uncertainty is caused by the fact that Lennon has occasionally been used as the English version of completely different Irish surnames, in particular O Lonan or O Lonagain ("Lenane" or "Lannigan") based in west Cork, and O Luinigh ("Lunney") originally from Donegal and now strongly associated with the adjoining Co. Fermanagh. The primary Irish source of Lennon, O Leannain, arose separately in east Co. Galway, in Co. Mayo, and in Co. Fermanagh. Historically, the most important were the Fermanagh family, who held land and ecclesiastical office in the parish of Inishmacsaint. Today, Lennon remains common in Ulster, but elsewhere has spread from its traditional homelands to become most frequent in the eastern province of Leinster.