bone of contention vs theme

bone of contention and theme both are nouns.

Word	Noun	Adjective	Verb	Adverb
bone of contention	Yes	No	No	No
theme	Yes	No	Yes	No

As nouns, theme is a hypernym of bone of contention; that is, theme is a word with a broader meaning than bone of contention:

Other hypernyms of bone of contention include subject, topic.

bone of contention (noun)	theme (noun)
the subject of a dispute	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

bone of contention (verb)	theme (verb)
	provide with a particular theme or motive