MonahanIrish From Irish Ó Manacháin meaning "descendant of Manacháin". The given name Manacháin meant "little monk", from manach "monk" and a diminutive suffix.
Monday 3Irish Anglicized form of Mac Giolla Eoin. The last part of the surname was mistakenly taken as the Gaelic word for "Monday", Luain.
MoriartyIrish From Irish Ó Muircheartach meaning "descendant of Muirchertach". This was the surname given by Sir Arthur Conan Doyle to a master criminal in the Sherlock Holmes series.
O'HaraIrish From the Irish Ó hEaghra, which means "descendant of Eaghra", Eaghra being a given name of uncertain origin. Supposedly, the founder of the clan was Eaghra, a 10th-century lord of Luighne. A famous fictional bearer of this surname is Scarlett O'Hara, a character in Margaret Mitchell's Gone With The Wind (1936).
TaggartIrish, Scottish Anglicized form of Irish Mac an tSagairt meaning "son of the priest". This name comes from a time when the rules of priestly celibacy were not strictly enforced.