ignis fatuus vs phantasy

ignis fatuus and phantasy both are nouns.

Word	Noun	Adjective	Verb	Adverb
ignis fatuus	Yes	No	No	No
phantasy	Yes	No	No	No

As nouns, phantasy is a hypernym of ignis fatuus; that is, phantasy is a word with a broader meaning than ignis fatuus:

Other hypernyms of ignis fatuus include fancy, fantasy, illusion.

ignis fatuus (noun)	phantasy (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