The other way round. If you have a name in Irish in front of you — on a gravestone, in a parish register, on a census return, at the top of a letter from a relative who kept the old form — this is what it became in English. 298 forms, listed by the root word, because the root is the part you can read and the prefix is the part that repeats.
Nearly every Irish surname is a prefix plus a root. The prefix tells you the kind of name; the root is the ancestor, the trade or the place. Find the root in the list below — it is what the names are sorted by.
It happens, and it is not a mistake in the record. Different clerks heard the same sound differently, and some families translated the meaning while their neighbours copied the sound. These are the ones on this site where a single Irish form is behind more than one English surname.
Darcy. It means “descendant of the dark one”, from dorcha, dark. The Norman family d'Arcy arrived separately and the two names converged in English spelling — the same surname today can have either behind it.
Smith, and also McGowan. Gabha is a smith, so Mac Gabhann is the son of the smith. The Mac Gabhann sept of Bréifne largely translated the name outright under English pressure, which is why so many Irish Smiths are not English at all.
Look up the root — the word after Ó or Mac — in the A–Z on this page. The root is the part that carries the meaning and the part that varies; the prefix only tells you whether the name is built on a descendant, a son, or a Norman place.
No, and this is a common confusion. Ó Cionnaith is Kenny and Mac Cionaoith is McKenna — different families, similar-looking roots, different prefixes. A name that differs only in prefix is a different name, not a variant spelling.
Because different clerks in different places heard the same sound differently, and because some families translated the meaning while others copied the sound. Mac Eochaidh gave both Keogh and Kehoe; Ó hAodha gave both Hayes and Hughes. Both are genuinely the same original name.
Almost always, for Gaelic names — the English spelling is a clerk's attempt at hearing it. But not for the de names, which are Norman and came with their own spelling, nor for planter surnames, which never had an Irish form and are not listed here.
The Irish forms here are the standard modern spellings, and Irish spelling was only standardised in the twentieth century. A name in a nineteenth-century register may look quite different — older forms carry letters the reform removed, and the same name can appear a dozen ways across the centuries. If the form in front of you is close but not identical, you have probably still found it.
Spoken audio is synthesised by ABAIR at Trinity College Dublin — a machine reading the name, not a recording of a speaker. For native speakers, Teanglann has recordings.
Know a form we have wrong, or one we are missing? Tell us — this is exactly the kind of thing families know and books do not. · The same list, English to Irish · What Ó and Mac actually mean · How to trace an Irish ancestor