I. bə(r)-ˈsərk, ˌbər-, -ˈzərk; ˈbər-ˌ noun
or ber·serk·er -ˈsər-kər, -ˈzər-; ˈbər-ˌ
Etymology: Old Norse berserkr, probably from ber- bear + serkr shirt
Date: 1818
1. : an ancient Scandinavian warrior frenzied in battle and held to be invulnerable
2. : one whose actions are recklessly defiant
II. adjective
Date: 1851
: frenzied , crazed — usually used in the phrase go berserk
sinister ravings of an imagination gone berserk — John Gruen
• berserk adverb
• ber·serk·ly adverb