mutav

1. colloq. derog. stupid; dumb; daft
   Jesi li mutav, ne vidiš da je crveno? — Are you dumb? Can't you see it's red?
2. colloq. silent; tongue-tied
   Što si tako mutav večeras, ništa ne pričaš? — Why are you so quiet tonight? You're not saying anything.
3. dated mute
   Njegov brat je bio mutav od rođenja. — His brother had been mute since birth.

The neutral word for “mute” is nem; mutav said of a person usually sounds rude.