science fiction vs fantasy

science fiction and fantasy both are nouns.

Word	Noun	Adjective	Verb	Adverb
science fiction	Yes	No	No	No
fantasy	Yes	No	Yes	No

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

science fiction: literary fantasy involving the imagined impact of science on society
fantasy: fiction with a large amount of imagination in it

Other hypernyms of science fiction include phantasy.

science fiction (noun)	fantasy (noun)
literary fantasy involving the imagined impact of science on society	imagination unrestricted by reality
	something many people believe that is false
	fiction with a large amount of imagination in it

science fiction (verb)	fantasy (verb)
	indulge in fantasies