evil spirit vs fiend

evil spirit and fiend both are nouns.

Word	Noun	Adjective	Verb	Adverb
evil spirit	Yes	No	No	No
fiend	Yes	No	No	No

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

evil spirit (noun)	fiend (noun)
a spirit tending to cause harm	a cruel wicked and inhuman person
	a person motivated by irrational enthusiasm (as for a cause)
	an evil supernatural being