(hə-l´sə-nāʹshən) noun. 1. a. False or distorted perception of objects or events with a compelling sense of their reality, usually resulting from a mental disorder or as a response to a drug. b. The objects or events so perceived. 2. A false or mistaken idea; a delusion, halusinasi, rayan: it wasn't a ghost, it was just a hallucination, itu bukannya hantu, itu hanya halusinasi.