The Collaborative International Dictionary of English v.0.48:
monogamousness \monogamousness\ n. The state of being monogamous; having one wife at a time. Syn: monogamy, monogyny. [WordNet 1.5]WordNet (r) 3.0 (2006):
monogamousness n 1: having only one spouse at a time [syn: monogamy, monogamousness]