The origin is disputed. A phonetically exact correspondence exists in Old Norse bjǫrn (“bear”), from Proto-Germanic *bernuz (more at *berô), but the English word is never used for "bear", and the Old Norse word is never used for "warrior". While it is not implausible that the term for a wild animal could become a poetic term for a warrior, Germanic scholars have been reluctant to accept any relationship between the two. Some consider it to be a variant of Old English bearn (“child, offspring, son", hence "boy, servant”), while others derive it from a Proto-Germanic *beron- (“carrier”) (hence "servant; man, warrior", more at baron). Celtic origin has also been considered; thus, Rhys took this to be a Germanic reflex of the Celtic title Brennus, and Bradley connected British Bernicia (Welsh brenhin, brenin).
The word has the form biorn in early Old English attestations; it survives into early Middle English as beorn and takes the variant spellings bern, berne, burn, burne, bearn, bieren, beern, beerne in later Middle English. Middle English usage often interchanges it with baron. As berne, it survives into the 16th century in Scottish dialect, but becomes indistinguishable from bairn.
beorn m (nominative plural beornas)