allusion, delusion, elusion, illusion

These words, somewhat alike in sound and spelling, have different meanings and uses. An allusion is an indirect reference or mention: "He made an allusion to a character in a TV melodrama." Delusion means "a false belief," one usually held as a result of self-deception. It is commonly used to refer to a person suffering from a mental disorder: "Bob suffers from delusions of grandeur." "Alice is under the delusion that she is Joan of Arc." Elusion, a rarely used word, means "an escape," "an evasion": "Not attending the meeting is an elusion of your obligation to vote." Illusion is related in meaning to delusion; it refers to a false mental image or idea, to something that is imagined and that may or may not be based on fact: "A mirage is an illusion." "At times, Charlie is under the illusion that he is a star football player." A delusion is more likely to be harmful or serious than is an illusion.