Leahy is an Irish surname, originating in Munster, and now found in counties Cork, Kerry, Limerick, and Tipperary.
It is usually an anglicised form of the Irish language surname Ó Laochdha ("descendant of Laochdha"),[1]: 191 which ultimately derives from Old Irish láechda, láech ("warrior-like, pertaining to a warrior") and appears as a personal sobriquet at least as early as the Book of Lismore (circa 1408–11).
[2] However, Leahy may also represent an anglicisation of less common names, including Mac Fhlaithimh and Ó Flaithimh, Mac an Leagha, Ó Leathaigh, Ó Liathaigh, Ó Líthe, Ó Laidhe, Ó Laidhigh, Ó Laithimh, Ó'Lathaigh, Ó Laithmhe, Ó Laochdha, Ó Laoi, Ó Laoidhigh, or Ó Laoithe.
[3] Not to be confused with Lahey which means "Ruler" and is a separate family lineage.
Other anglicised forms of the name include Leahey, Lahy, Leehy, Leehey, Lahaie, Lahaye, Lehait,[4]: 15 [1]: 188 [5]: 104–106 Claffey, Laffey, and Lee.