having the qualities of a devil; devilish; fiendish; outrageously wicked: a diabolic plot.

Is diabolically a word?

di·a·bol·i·cal

adj. 1. Of, concerning, or characteristic of the devil; satanic.

Is it diabolic or diabolical?

As adjectives the difference between diabolical and diabolic

is that diabolical is extremely wicked or cruel while diabolic is showing wickedness typical of a devil.