dream vs mental imagery

dream and mental imagery both are nouns.

Word	Noun	Adjective	Verb	Adverb
dream	Yes	No	Yes	No
mental imagery	Yes	No	No	No

As nouns, mental imagery is a hypernym of dream; that is, mental imagery is a word with a broader meaning than dream:

Other hypernyms of dream include imagery, imagination, imaging.

dream (noun)	mental imagery (noun)
a series of mental images and emotions occurring during sleep	the ability to form mental images of things or events
imaginative thoughts indulged in while awake
a fantastic but vain hope (from fantasies induced by the opium pipe)
a state of mind characterized by abstraction and release from reality
a cherished desire
someone or something wonderful

dream (verb)	mental imagery (verb)
have a daydream; indulge in a fantasy
experience while sleeping