incubus vs fiend

incubus and fiend both are nouns.

Word	Noun	Adjective	Verb	Adverb
incubus	Yes	No	No	No
fiend	Yes	No	No	No

As nouns, fiend is a hypernym of incubus; that is, fiend is a word with a broader meaning than incubus:

incubus: a male demon believed to lie on sleeping persons and to have sexual intercourse with sleeping women
fiend: an evil supernatural being

Other hypernyms of incubus include daemon, daimon, demon, devil.

incubus (noun)	fiend (noun)
a male demon believed to lie on sleeping persons and to have sexual intercourse with sleeping women	a cruel wicked and inhuman person
someone who depresses or worries others	a person motivated by irrational enthusiasm (as for a cause)
a situation resembling a terrifying dream	an evil supernatural being