/ bəˈzɜːk; -ˈsɜːk; NAmE bərˈzɜːrk; -ˈsɜːrk/ adjective [ not usually before noun ]
1.
very angry, often in a violent or uncontrolled way :
He went berserk when he found out where I'd been.
2.
very excited :
People were going berserk with excitement.
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WORD ORIGIN
early 19th cent. (originally as a noun denoting a wild Norse warrior who fought with frenzy): from Old Norse berserkr (noun), probably from birn- , bjorn + serkr coat, but also possibly from berr bare (i.e. without armour).