Where does “O’Brien” come from?

O’Brien (English) comes from Irish Ó Briain, from English Brian, from Irish Brian, from Proto-Brythonic brɨɣėnt, from Proto-Celtic brigantī, from Proto-Indo-European bʰérǵʰonts, from Proto-Indo-European bʰerǵʰ- — to rise; high, lofty; hill, mountain.

Ancestry of “O’Brien”, step by step

StepLanguageWordMeaning
1IrishÓ Briain
2EnglishBrianTo keep fire at the mouth of (as of an oven), to give light or to preserve heat
3IrishBrian
4Proto-Brythonicbrɨɣėntprivilege, birthright
5Proto-Celticbrigantīsomething high or elevated; an exalted person
6Proto-Indo-Europeanbʰérǵʰontshigh
7Proto-Indo-Europeanbʰerǵʰ-to rise; high, lofty; hill, mountain
Every word from Proto-Indo-European bʰerǵʰ-Every word from Proto-Indo-European bʰérǵʰontsEvery word from Proto-Celtic brigantī