1. Destructively or frenetically violent: a berserk worker who started smashing all the windows.
2. Mentally or emotionally upset; deranged: berserk with grief.
3. Informal Unrestrained, as with enthusiasm or appetite; wild: berserk over chocolates.

1. One that is violent, upset, or unrestrained.
2. A berserker.

Word History: When we say that we are going berserk, we may not realize how extreme a state this might be. Our adjective comes from the noun berserker, or berserk, which is from the Old Norse word berserkr, "a wild warrior or champion." Such warriors wore hides of bears, which explains the probable origin of berserkr as a compound of *bera, "bear," and serkr, "shirt, coat." These berserkers became frenzied in battle, howling like animals, foaming at the mouth, and biting the edges of their iron shields. Berserker is first recorded in English in the early 19th century, long after these wild warriors ceased to exist.