Describes a fierce, brutal, and merciless nature, often used for people, actions, or expressions. Somewhat literary and emphatic.
Everyone trembled at his fiendish expression.
The crime was so brutal that I was left speechless.
Composed of 獰 (どう, 'ferocious, bad-tempered') and 悪 (あく, 'evil, bad'). The combination directly conveys a fierce and wicked nature. The exact historical derivation is uncertain, but the kanji components are transparent.