polemic vs contention

polemic and contention both are nouns.

Word	Noun	Adjective	Verb	Adverb
polemic	Yes	Yes	No	No
contention	Yes	No	No	No

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

polemic: a controversy (especially over a belief or dogma)
contention: a contentious speech act; a dispute where there is strong disagreement

Other hypernyms of polemic include arguing, argument, contestation, controversy, disceptation, disputation, tilt.

polemic (noun)	contention (noun)
a controversy (especially over a belief or dogma)	the act of competing as for profit or a prize
a writer who argues in opposition to others (especially in theology)	a contentious speech act; a dispute where there is strong disagreement
	a point asserted as part of an argument

polemic (adjective)	contention (adjective)
of or involving dispute or controversy