- 1 [countable, uncountable] a false idea or belief, especially about someone or about a situation She's under the illusion that (= believes wrongly that) she'll get the job. The new president has no illusions about the difficulties facing her country (= she knows that the country has serious problems). Ihave no illusions about her feelings for me (= I know the truth is that she does not love me). He could no longer distinguish between illusion and reality. I don't want to have my illusions shattered!
- 2 [countable] something that seems to exist but in fact does not, or seems to be something that it is not Mirrors in a room often give an illusion of space. The idea of absolute personal freedom is an illusion.