defiinition of delusion from Random House Dictionary | ward's Blog

de·lu·sion  (di loo zhen), n.
1.    an act or instance of deluding.
2.    the state of being deluded.
3.    a false belief or opinion: delusions of grandeur.
4.    Psychiatry. a fixed false belief that is resistant to reason or confrontation with actual fact: a paranoid delusion.
[1375-1425; late ME < L di loo zhen- (s. of dilusio), equiv. to delus(us) (ptp. of di ludere; see DELUDE) + -ion- -ION]
-de·lu' sion·al, de·lu' sion·ary, adj.
-Syn.1. deception. See illusion.

de·lude (di lood'), v.t., -lud·ed, -lud·ing.
1.    to mislead the mind or judgment of; deceive: His conceit deluded him into believing he was important.
2.    Obs. to mock or frustrate the hopes or aims of.
3.    Obs. to elude; evade.
[1400-50; late ME deluden < L deludere to play false, equiv. to de- DE- + ludere to play]
-de·lud' er, n.
-de·lud' ing·ly, adv.
-Syn.1. beguile, cozen, dupe, cheat, defraud, gull.