rheology vs natural philosophy

rheology and natural philosophy both are nouns.

Word	Noun	Adjective	Verb	Adverb
rheology	Yes	No	No	No
natural philosophy	Yes	No	No	No

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

rheology: the branch of physics that studies the deformation and flow of matter
natural philosophy: the science of matter and energy and their interactions

Other hypernyms of rheology include physics.

rheology (noun)	natural philosophy (noun)
the branch of physics that studies the deformation and flow of matter	the science of matter and energy and their interactions