a ghost or the spirit of a dead person being seen

ghost

something which one seems to see or experience during sleep

illusion, vision

wild or extravagant creative thought or mental pictures

imagination, dream

something invented or imagined

creation in one's mind

unusual and unexpected

something, someone very abnormal

(the seeing of) something that does not really exist; a false or impossible idea

false appearance; false belief

(the ability to create) mental pictures of a person, situation etc that has not been experienced

power to create in one's mind

a ghost

ghost; figment of the imagination