polygamy vs matrimony

polygamy and matrimony both are nouns.

Word	Noun	Adjective	Verb	Adverb
polygamy	Yes	No	No	No
matrimony	Yes	No	No	No

As nouns, matrimony is a hypernym of polygamy; that is, matrimony is a word with a broader meaning than polygamy:

polygamy: the condition or practice of having more than one spouse at a time
matrimony: the state of being a married couple voluntarily joined for life (or until divorce)

Other hypernyms of polygamy include marriage, spousal relationship, union, wedlock.

polygamy (noun)	matrimony (noun)
the condition or practice of having more than one spouse at a time	the ceremony or sacrament of marriage
	the state of being a married couple voluntarily joined for life (or until divorce)