will-o'-the-wisp vs fantasy

will-o'-the-wisp and fantasy both are nouns.

Word	Noun	Adjective	Verb	Adverb
will-o'-the-wisp	Yes	No	No	No
fantasy	Yes	No	Yes	No

As nouns, fantasy is a hypernym of will-o'-the-wisp; that is, fantasy is a word with a broader meaning than will-o'-the-wisp:

Other hypernyms of will-o'-the-wisp include fancy, illusion, phantasy.

will-o'-the-wisp (noun)	fantasy (noun)
an illusion that misleads	imagination unrestricted by reality
a pale light sometimes seen at night over marshy ground	something many people believe that is false
	fiction with a large amount of imagination in it

will-o'-the-wisp (verb)	fantasy (verb)
	indulge in fantasies