atomic spectrum vs natural philosophy

atomic spectrum and natural philosophy both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic spectrum	Yes	No	No	No
natural philosophy	Yes	No	No	No

atomic spectrum (noun)	natural philosophy (noun)
(physics) a spectrum of radiation caused by electron transitions within an atom; the series of spectrum lines is characteristic of the element	the science of matter and energy and their interactions