Entry 1 sense Webster, 1913 Illusory /ĭ-lo͞o′sə-rē/ · Il·lu·so·ry · IPA /ɪˈlu.sə.ɹi/ 01 a. Deceiving, or tending of deceive; fallacious; illusive; as, illusory promises or hopes. 1. Deceiving, or tending of deceive; fallacious; illusive; as, illusory promises or hopes.