say it: il-OO-zhuhn
illusion is a noun meaning "an erroneous mental representation". It carries 4 recorded senses.
an erroneous mental representation
something many people believe that is false
“they have the illusion that I am very wealthy”
an illusory feat; considered magical by naive observers
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for illusion come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.