flying saucer vs apparition

flying saucer and apparition both are nouns.

Word	Noun	Adjective	Verb	Adverb
flying saucer	Yes	No	No	No
apparition	Yes	No	No	No

As nouns, apparition is a hypernym of flying saucer; that is, apparition is a word with a broader meaning than flying saucer:

flying saucer: an (apparently) flying object whose nature is unknown; especially those considered to have extraterrestrial origins
apparition: something existing in perception only

Other hypernyms of flying saucer include fantasm, phantasm, phantasma, phantom, shadow.

flying saucer (noun)	apparition (noun)
an (apparently) flying object whose nature is unknown; especially those considered to have extraterrestrial origins	an act of appearing or becoming visible unexpectedly
	something existing in perception only
	the appearance of a ghostlike figure
	a ghostly appearing figure