ber·serk /bərˈsɜrk, -ˈzɜrk/
1. violently or destructively frenzied; wild; crazed; deranged: He suddenly went berserk.
2. (sometimes initial capital letter) Scandinavian Legend. Also, ber·serk·er. an ancient Norse warrior who fought with frenzied rage in battle, possibly induced by eating hallucinogenic mushrooms.
[Origin: 1865–70; < ON berserkr, equiv. to ber- (either *ber-, base of bjǫrn bear2 or berr bare1) + serkr sark, shirt, armor]