The commonly misused words elude, allusion and illusion share a common root word (Latin ludere: to play), but their meanings aren’t similar at all. Fortunately, recognizing the prefixes can help keep these two words separate in your mind.
The Latin prefix e means “out,” so elude originally suggested the end of a game or a sword fight, where a clever winner tricked his opponent by “playing out.” A fugitive can elude his pursuers by making them look for him outside of where he really is.
The prefix a or ad often comes from the Latin ad, which means “to.” For example, an adjunct professor is a part-time instructor who is “joined to” the faculty to teach a few classes. So an allusion is an indirect reference “played to” something else, such as a quotation that you expect your readers will recognize without having to be told where it came from.
The prefix in or sometimes il or im often comes from the Latin in, which means “at, in, toward,” among other things. It gives illusion the meaning of “play with.” An illusion is something that isn’t real – somebody is playing with your mind and trying to fool you.