fiend vs incubus

fiend and incubus both are nouns.

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

As nouns, incubus is a hyponym of fiend; that is, incubus is a word with a more specific, narrower meaning than fiend:

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

Other hyponyms of fiend include succuba, succubus, dibbuk, dybbuk.

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