nihilistic delusion vs delusion

nihilistic delusion and delusion both are nouns.

Word	Noun	Adjective	Verb	Adverb
nihilistic delusion	Yes	No	No	No
delusion	Yes	No	No	No

As nouns, delusion is a hypernym of nihilistic delusion; that is, delusion is a word with a broader meaning than nihilistic delusion:

nihilistic delusion: the delusion that things (or everything, including the self) do not exist; a sense that everything is unreal
delusion: (psychology) an erroneous belief that is held in the face of evidence to the contrary

Other hypernyms of nihilistic delusion include psychotic belief.

nihilistic delusion (noun)	delusion (noun)
the delusion that things (or everything, including the self) do not exist; a sense that everything is unreal	the act of deluding; deception by creating illusory ideas
	a mistaken or unfounded opinion or idea
	(psychology) an erroneous belief that is held in the face of evidence to the contrary