Meaning

noun one of the ancient Norse warriors legendary for working themselves into a frenzy before a battle and fighting with reckless savagery and insane fury

adjective frenzied as if possessed by a demon

originBorrowed from Old Norse berserkr (“Norse warrior who fights with frenzy”), probably from bjǫrn (“bear”) + serkr (“coat; shirt”), referring to the bearskins worn by the warriors. Bjǫrn is possibly ultimately derived from Proto-Indo-European *bʰerH- (“brown”); and serkr from Proto-Indo-European *ser- (“to bind, tie together; thread”). Alternatively, it has been suggested that the first element of…

Etymology from Wiktionary, CC BY-SA 3.0