today's word: monogamy

Monogamy /Gr. μονός+γάμος (monos+gamos) - one+marriage/ a form of marriage in which an individual has only one spouse at any one time.[1] In current usage monogamy often refers to having one sexual partner irrespective of marriage or reproduction. The term is also applied to the social behavior of some animals, referring to the state of having only one mate at any one time.

example: Bigamy is having one wife too many. Monogamy is the same.