theme vs root word

theme and root word both are nouns.

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

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

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

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

theme (noun)	root word (noun)
a unifying idea that is a recurrent element in literary or artistic work	(linguistics) the form of a word after all affixes are removed
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

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