Take a look at these women's names:

Meabh O'Hare
Michelle O'Brien

Lasairfhíona Ní Chonaola
Maighread Ni Dhomhnaill
Tríona Ní Dhómhnaill
Máire Ní Chathasaigh
Eilín Ní Chearna
Eilís Ní Shúilleabháin

Aine Uí Laoithe
Aine Ui Cheallaigh

I gathered these from www.madfortrad.com in their CD Shop.

1. Are Ní & Uí proper feminine forms of O' (or Mc)?

2. Regarding women, when would you use O' vs. Ní, Uí.

3. Doesn't Ní mean "not"?

Uí is used before the surname of the husband: Áine Uí Laoithe = Áine wife of man whose surname is Ó Laoithe.

Ní is used before the surname of the father: Lasairfhíona Ní Chonaola = Lasairfhíona daughter of a man whose surname is Ó Conaola.
Actually, many women who use their Irish-language surname don’t change it when they get married, so a woman whose surname begins with Ní may be married.

O' is used with the English version of the name (in English they don't use Ní). Some women have a surname with Ó in Irish, which is very odd and I always wondered why (because sometimes these women know Irish so they should know Ó becomes Ní...). If someone knows...

Mac becomes Nic for a woman (her maiden name): if Seán Mac Mathúna has a daughter, her surname will be Nic Mhathúna.

Ní means ’not’ before a verb, but Ní before a surname derives from Iníon Uí (daughter of Ó...), so these 2 words are spelt the same way, by mere chance, but they are completely different.

Perhaps "o" is used in cases of divorce where the woman is not the wife or daughter

quote:

If someone knows...

Perhaps it's a feminist view:
Not to be only the daughter of a descendant but to be a direct and independent descendant of an ancestor.

quote:

so these 2 words are spelt the same way, by mere chance, but they are completely different.

There's even a third (and different) word: ní = thing.

Lars

b'fheidir,

Wouldn't make sense, since "ó" would imply "grandson of"

which she definitely is not.

Antaine- "O" today means more exactly descended from. Very few O'Laughlins today would be true grandsons of the original Laughlin.Also "Ni" and "Ui" are only used with the Gaelic version of the surname. O'Hare and O'Brien are the English versions

quote:

"O" today means more exactly descended from.

As far as I know, it just means "grandson". It’s not the preposition "ó", but a noun that is etymologically different.

ODonail states that as used in surnames it means grandson and descendant

quote:

Wouldn't make sense, since "ó" would imply "grandson of"

Yes, of course, it would not make sense.
But "political correctness" doesn't make sense in other languages, too.

Lars

patronymic nomenclature is somewhat alien to english speakers. Most english speakers I know are amazed to discover how names are handled in Iceland or used to be in Norway.

I would think that following the tradition, the woman would change her name from Uí back to Ní or Nic.