ber·serk 
(bər-sûrk, -zûrk, bə-)
(bər-sûrk, -zûrk, bə-)adj.
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.
n.
1. One that is violent, upset, or unrestrained.
2. A berserker.
[Back-formation from BERSERKER.]
ber·serk adv.
ber·serkly adv.