Why are some of my old Irish relatives named with Mc' or O'?

McDonnell , O'Donnell. what does Mc' & O' mean?
apparently this way of naming goes back for many years?

Thanks, this I brings up another question on the same subject. If my name is "O'Donnell" am I related to all the O'Donnell's/McDonnell's or was there different 'Donnell's" in the beginning of it all?

Mac (Mc) means son of, so MacDonnell means 'son of Donnell'. The McDonnells share a common ancestor called Donnell who was probably a chieftan or a king centuries ago.

History of the McDonnell name here:
http://www.ireland.com/ancesto... Report It

Mc is short for "mac", the Irish word for "son". When used in a name it means "son of". "脫" is the Irish word for "from", and when used in a name it means "grandson of".

There would be different branches of each family. You are most likely not related to everyone who has the same surname as you.

My last name is O'Dell because my family came from the House of Dell.
Morris Dell to be exact.
It is just an extended family name for those of years past who were proud of their family name and wanted to honor them.

Mac means 'son of' - so 'MacCarthy' means 'son of Carthy'. For daughters is was 'Nic', for wives it was 'Ui'.

O is more 'from', as in 'from the retinue of' or 'follower of'. Likewise for daughters it was 'Ni'.

The MC'S originate from the Scottish that's why,The O'S are the Irish

You have some good answers there - and if you have any ancestors with the Fitz in front of their name it means 'bastard son of...' tho in those days it wasn't a curse...