monogamy (n.)

1610s, "practice of marrying only once in a lifetime," from French monogamie, from Late Latin monogamia, from Greek monogamia "single marriage," from monogamos "marrying only once," from monos "single, alone" (from PIE root *men- (4) "small, isolated") + gamos "marriage" (see gamete). As "condition of being married to only one person at a time," by 1708.