marriage vs monandry

marriage and monandry both are nouns.

Word	Noun	Adjective	Verb	Adverb
marriage	Yes	No	No	No
monandry	Yes	No	No	No

As nouns, monandry is a hyponym of marriage; that is, monandry is a word with a more specific, narrower meaning than marriage:

marriage: the state of being a married couple voluntarily joined for life (or until divorce)
monandry: the state of having only one husband at a time

marriage (noun)	monandry (noun)
the act of marrying; the nuptial ceremony	the state of having only one husband at a time
two people who are married to each other
the state of being a married couple voluntarily joined for life (or until divorce)
a close and intimate union