monogamy vs monogamousness

monogamy and monogamousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
monogamy	Yes	No	No	No
monogamousness	Yes	No	No	No

As nouns, monogamy and monogamousness are synonyms defined as:

monogamy and monogamousness: the practice or state of having only one spouse at a time

monogamy (noun)	monogamousness (noun)
the practice or state of having only one spouse at a time	the practice or state of having only one spouse at a time