demonic vs fiendish

demonic and fiendish both are adjectives.

Word	Noun	Adjective	Verb	Adverb
demonic	No	Yes	No	No
fiendish	No	Yes	No	No

As adjectives, demonic and fiendish are synonyms defined as:

demonic and fiendish: extremely evil or cruel; expressive of cruelty or befitting hell

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

demonic (adjective)	fiendish (adjective)
extremely evil or cruel; expressive of cruelty or befitting hell	extremely evil or cruel; expressive of cruelty or befitting hell