The Oxford Thesaurus An A-Z Dictionary of Synonyms - illusionn.

1) deception, delusion, fancy, misconception, misapprehension, fallacy, error, mistake, mistaken or false impression: He is labouring under the illusion that he is a great pianist. 2) fantasy, day-dream, hallucination, phantasm, phantom, chimera, phantasmagoria, mirage, aberration, vision, spectre, figment of the imagination, will-o'-the-wisp, ignis fatuus: For years after he died, she had the illusion of seeing her father everywhere.