root word vs theme

root word and theme both are nouns.

Word	Noun	Adjective	Verb	Adverb
root word	Yes	No	No	No
theme	Yes	No	Yes	No

As nouns, root word and theme are synonyms defined as:

root word and theme: (linguistics) the form of a word after all affixes are removed

Other synonyms of root word include base, radical, root, stem.

root word (noun)	theme (noun)
(linguistics) the form of a word after all affixes are removed	a unifying idea that is a recurrent element in literary or artistic work
	the subject matter of a conversation or discussion
	an essay (especially one written as an assignment)
	(music) melodic subject of a musical composition
	(linguistics) the form of a word after all affixes are removed

root word (verb)	theme (verb)
	provide with a particular theme or motive