📒 a false idea or belief, especially about somebody or about a situation
under the illusion that… She's under the illusion that (= believes wrongly that) she'll get the job.
illusion about something The new president has no illusions about the difficulties facing her country (= she knows that the country has serious problems).
I have no illusions about her feelings for me (= I know the truth is that she does not love me).
📒 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.
It turned out that their happy marriage was all an illusion.