Definitions for diabolical
devilish, diabolic, diabolical, mephistophelian, mephistophelean(adj)
showing the cunning or ingenuity or wickedness typical of a devil
"devilish schemes"; "the cold calculation and diabolic art of some statesmen"; "the diabolical expression on his face"; "a mephistophelian glint in his eye"
demonic, diabolic, diabolical, fiendish, hellish, infernal, satanic, unholy(adj)
extremely evil or cruel; expressive of cruelty or befitting hell
"something demonic in him--something that could be cruel"; "fires lit up a diabolic scene"; "diabolical sorcerers under the influence of devils"; "a fiendish despot"; "hellish torture"; "infernal instruments of war"; "satanic cruelty"; "unholy grimaces"
Extremely wicked or cruel.
Of or concerning the devil; satanic.
pertaining to the devil; resembling, or appropriate, or appropriate to, the devil; devilish; infernal; impious; atrocious; nefarious; outrageously wicked; as, a diabolic or diabolical temper or act