Gaelic surname

Onomastics is an important source of information on the early Celts, as Greco-Roman historiography recorded Celtic names before substantial written information becomes available in any Celtic language.

Like Germanic names, early Celtic names are often .

Some information on prehistoric Celtic polytheism can be drawn from names in Irish and Welsh mythology, which often continue older theonyms:

Many surnames of Gaelic origin in Ireland and the other Celtic nations, derive from ancestors' names, nicknames, or descriptive names. In the first group can be placed surnames such as MacMurrough and MacCarthy, derived from patronymics, or O'Brien and O'Grady, derived from ancestral names.

Gaelic surnames derived from nicknames include Ó Dubhda (from Aedh ua Dubhda—Aedh, the dark one), O'Doherty (from Ó Dochartaigh, "destroyer" or "obtrusive"), Garvery (garbh, "rough" or "nasty"), Manton (mantach, "toothless"), Bane (bán, "white", as in "white hair"), Finn (fionn, "fair", as in "fair hair") and Kennedy ("cennedie", as in "ugly head")

Very few Gaelic surnames are derived from placenames or venerated people/objects. Among those that are included in this small group, several can be shown to be derivations of Gaelic personal names or surnames. One notable exception is Ó Cuilleáin or O'Collins (from cuileann, "holly") as in the Holly Tree, considered one of the most sacred objects of pre-Christian Celtic culture. Another is Walsh (Irish: Breatnach), meaning Welsh.

In areas where certain family names are extremely common, extra names are added that sometimes follow this archaic pattern. In Ireland, for example, where Murphy is an exceedingly common name, particular Murphy families or extended families are nicknamed, so that Denis Murphy's family were called The Weavers and Denis himself was called Denis "The Weaver" Murphy. (See also O'Hay.)

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