Where does “աղբայր” come from?

աղբայր (Old Armenian) comes from Old Armenian եղբայր, from Proto-Indo-European bʰréh₂tēr — brother.

Ancestry of “աղբայր”, step by step

Step	Language	Word	Meaning
1	Old Armenian	եղբայր	brother; kinsman, relative; friar, monk
2	Proto-Indo-European	bʰréh₂tēr	brother

աղբայր — Etymology, Origin & Word History | Etymology Explorer