Where does “b” come from?

b (Old Irish) comes from Proto-Celtic abū, from Proto-Indo-European h₂ep- — water, body of water.

Ancestry of “b”, step by step

StepLanguageWordMeaning
1Proto-Celticabūriver
2Proto-Indo-Europeanh₂ep-water, body of water
Every word from Proto-Indo-European h₂ep- →Every word from Proto-Celtic abū →