polygamy vs polygamous

polygamy is a noun but polygamous is not a noun.

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

polygamy (noun)	polygamous (noun)
the condition or practice of having more than one spouse at a time

polygamy (adjective)	polygamous (adjective)
	having more than one mate at a time; used of relationships and individuals
	having several forms of gametoecia on the same plant