natural science vs science

natural science and science both are nouns.

Word	Noun	Adjective	Verb	Adverb
natural science	Yes	No	No	No
science	Yes	No	No	No

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

natural science: the sciences involved in the study of the physical world and its phenomena
science: a particular branch of scientific knowledge

Other hypernyms of natural science include scientific discipline.

natural science (noun)	science (noun)
the sciences involved in the study of the physical world and its phenomena	a particular branch of scientific knowledge
	ability to produce solutions in some problem domain