Where does “Mac Néill” come from?

Mac Néill (Scottish Gaelic) comes from Scottish Gaelic Niall, from Old Irish Níall.

Ancestry of “Mac Néill”, step by step

Step	Language	Word	Meaning
1	Scottish Gaelic	Niall	possibly "the champion
2	Old Irish	Níall	—

Mac Néill — Etymology, Origin & Word History | Etymology Explorer