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English definition of “illusion”

illusion

noun [C]  /ɪˈlu·ʒən/ us  
an idea or belief that is not true, or something that is not what it seems to be: We have no illusions about how difficult the job will be. [+ that clause] I was under the illusion that trains ran frequently on weekends (= I wrongly believed this). They managed to create the illusion of space in a tiny apartment.
illusory
adjective  /ɪˈlu·sə·ri, -zə·ri/ us  
Her fears were illusory.
(Definition of illusion from the Cambridge Academic Content Dictionary © Cambridge University Press)
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