define diabolical
Diabolical may refer to: 1  evil, the profound immorality, especially when regarded as a supernatural force, for example in religious belief. 2  the Devil, believed in many religions, myths and cultures to be a supernatural entity that is the personification of evil and the enemy of God and humankind. Diabolical (album) (1998), a studio album by the Swedish melodic-black-metal band Naglfar.