delusion vs mental condition

delusion and mental condition both are nouns.

Word	Noun	Adjective	Verb	Adverb
delusion	Yes	No	No	No
mental condition	Yes	No	No	No

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

delusion: (psychology) an erroneous belief that is held in the face of evidence to the contrary
mental condition: (psychology) a mental condition in which the qualities of a state are relatively constant even though the state itself may be dynamic

Other hypernyms of delusion include mental state, psychological condition, psychological state.

delusion (noun)	mental condition (noun)
the act of deluding; deception by creating illusory ideas	(psychology) a mental condition in which the qualities of a state are relatively constant even though the state itself may be dynamic
a mistaken or unfounded opinion or idea
(psychology) an erroneous belief that is held in the face of evidence to the contrary