ignis fatuus vs illusion

ignis fatuus and illusion both are nouns.

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

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

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

ignis fatuus (noun)	illusion (noun)
an illusion that misleads	the act of deluding; deception by creating illusory ideas
a pale light sometimes seen at night over marshy ground	an illusory feat; considered magical by naive observers
	something many people believe that is false
	an erroneous mental representation