natural philosophy vs mass-energy equivalence

natural philosophy and mass-energy equivalence both are nouns.

Word	Noun	Adjective	Verb	Adverb
natural philosophy	Yes	No	No	No
mass-energy equivalence	Yes	No	No	No

natural philosophy (noun)	mass-energy equivalence (noun)
the science of matter and energy and their interactions	(physics) the principle that a measured quantity of mass is equivalent (according to relativity theory) to a measured quantity of energy