na-adjective, noun
Literary or formal word describing extreme cruelty, violence, or ferocity. Not common in everyday speech; more likely in written descriptions of brutal acts or fierce animals.
その猛悪な犯罪に町中が震え上がった。
The whole town trembled at the atrocious crime.
猛悪な獣が村を襲ったという記録が残っている。
There is a record that a ferocious beast attacked the village.