Hallucination

Part of speech: noun (n.)

1. The act of hallucinating; a wandering of the mind; error; mistake; a blunder. This must have been the hallucination of the transcriber. Addison.

2. The perception of objects which have no reality, or of sensations which have no corresponding external cause, arising from disorder or the nervous system, as in delirium tremens; delusion. Hallucinations are always evidence of cerebral derangement and are common phenomena of insanity. W. A. Hammond.