/ dɪˈluːʒn; NAmE / noun
1.
[ C ] a false belief or opinion about yourself or your situation :
the delusions of the mentally ill
Don't go getting delusions of grandeur (= a belief that you are more important than you actually are) .
2.
[ U ] the act of believing or making yourself believe sth that is not true
••
WORD ORIGIN
late Middle English (in the sense act of deluding or of being deluded ): from late Latin delusio(n-) , from the verb deludere to mock, from de- (with pejorative force) + ludere to play.