Other forms: hallucinated; hallucinating; hallucinates
To hallucinate is to see or hear something that's not really there. If you hallucinate, it's a bit like dreaming while being awake.
When someone hallucinates, what they're perceiving seems very real and vivid, although it's not. Many different things can cause a person to hallucinate, including drugs, mental illness, damage to the brain, and even lack of adequate sleep. Some people hallucinate regularly, if mildly, just as they're falling asleep at night. The original meaning of hallucinate was "deceive," from the Latin hallucinatus, "wander in the mind."