fantasy world vs fantasy

fantasy world and fantasy both are nouns.

Word	Noun	Adjective	Verb	Adverb
fantasy world	Yes	No	No	No
fantasy	Yes	No	Yes	No

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

fantasy world: something existing solely in the imagination (but often mistaken for reality)
fantasy: imagination unrestricted by reality

Other hypernyms of fantasy world include phantasy.

fantasy world (noun)	fantasy (noun)
something existing solely in the imagination (but often mistaken for reality)	imagination unrestricted by reality
	something many people believe that is false
	fiction with a large amount of imagination in it

fantasy world (verb)	fantasy (verb)
	indulge in fantasies