pipe dream vs fantasy

pipe dream and fantasy both are nouns.

Word	Noun	Adjective	Verb	Adverb
pipe dream	Yes	No	No	No
fantasy	Yes	No	Yes	No

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

pipe dream: a fantastic but vain hope (from fantasies induced by the opium pipe)
fantasy: imagination unrestricted by reality

Other hypernyms of pipe dream include phantasy.

pipe dream (noun)	fantasy (noun)
a fantastic but vain hope (from fantasies induced by the opium pipe)	imagination unrestricted by reality
	something many people believe that is false
	fiction with a large amount of imagination in it

pipe dream (verb)	fantasy (verb)
	indulge in fantasies