natural philosophy vs principle of equivalence

natural philosophy and principle of equivalence both are nouns.

Word	Noun	Adjective	Verb	Adverb
natural philosophy	Yes	No	No	No
principle of equivalence	Yes	No	No	No

natural philosophy (noun)	principle of equivalence (noun)
the science of matter and energy and their interactions	(physics) the principle that an observer has no way of distinguishing whether his laboratory is in a uniform gravitational field or is in an accelerated frame of reference