hellish vs diabolic

hellish and diabolic both are adjectives.

Word	Noun	Adjective	Verb	Adverb
hellish	No	Yes	No	No
diabolic	No	Yes	No	No

As adjectives, hellish and diabolic are synonyms defined as:

hellish and diabolic: extremely evil or cruel; expressive of cruelty or befitting hell

Other synonyms of hellish include demonic, diabolical, fiendish, infernal, satanic, unholy.

hellish (adjective)	diabolic (adjective)
extremely evil or cruel; expressive of cruelty or befitting hell	extremely evil or cruel; expressive of cruelty or befitting hell
(informal) very unpleasant	showing the cunning or ingenuity or wickedness typical of a devil