Di'a-bōl'ie or Di'a-bōl'ie-al, a.

a. [Gr. διαβολικός, slanderous, devilish, Lat. diabolicus, Fr. diabolique, Pr. diabolic, diabolical, Sp., Pg., & It. diabolico. See DEVIL.] Pertaining to the devil; resembling, or appropriate to, the devil; devilish; infernal; impious; atrocious; nefarious; outrageously wicked; as, a diabolical temper or action. “The diabolical institution.” Motley.