The noun allusion means "an indirect reference to a person, event, or thing." Illusion is a noun that means "false impression." See also:
The president spoke of "hills to climb" and seeing "the valley below," biblical allusions to Israel's escape from slavery. Some listeners felt that his hopeful message was based, unfortunately, on an illusion.
"They are layered, so that an episode you saw when you were a kid was funny but when you are in high school you start noticing some of the sexual word play and all that sort of thing. And when you get your Ph.D in comparative literature and you watch the same episode, you’re suddenly understanding some of the literary illusions and philosophic illusions."
"I just wanted to point out that the word you want is literary ALLUSIONS and philosophic ALLUSIONS. Granted, I like a good literary illusion (though I’m not waiting in line for it)."
(John, "Good, Bad, and Ugly: Reader Reaction to Reuters News," July 23, 2007)
(a) A pleasant ______ is better than a harsh reality.
(b) The mayor's remark "Ich bin ein Springfielder" was an ______ to President John Kennedy's famous speech in West Berlin.