The Collaborative International Dictionary of English v.0.48:
Monogamist \Mo*nog"a*mist\, n. One who practices or upholds monogamy. --Goldsmith. [1913 Webster]WordNet (r) 3.0 (2006):
monogamist n 1: someone who practices monogamy (one spouse at a time) [syn: monogamist, monogynist]