Webster's Revised Unabridged Dictionary · 1913

Diabolic

Diabolic , adjective

[Latin diabolicus, Greek diaboliko`s devilish, slanderous: compare French diabolique. See Devil.]

1.
Pertaining to the devil; resembling, or appropriate, or appropriate to, the devil; befitting hell or satan; devilish; infernal; impious; as, a diabolic or diabolical temper or act; the diabolical expression on his face; fires lit up a diabolic scene.
Diabolic power. — Milton
The diabolical institution. — Motley
2.
showing a wicked cunning or ingenuity; as, the cold calculation and diabolic art of some statesmen.
3.
extremely evil or cruel; atrocious; outrageously wicked; as, diabolical sorcerers under the influence of devils; diabolical torturers taking pleasure in their craft.

Also: Diabolical