Postnuptial Agreement Definition: A separation agreement. Related Terms: Separation Agreement, Marriage Agreement An agreement drafted and entered into between two separating spouses in contemplation of their separation. In Hewett v Gott 132 Kan. 168 (1931), the Supreme Court of Kansas distinguished this from a marriage agreement (antenuptial) as follows: "An antenuptial contract is an agreement in contemplation of marriage, whereas a postnuptial contract is generally one in contemplation of separation. The former is providing and planning for a union of interest with some property modifications; the latter for a complete disunion of all domestic and property interests." Categories & Topics: Family Law Dictionary Find you are constantly looking up definitions? Try our search provider (works in most modern browsers) If you find an error or omission in Duhaime's Legal Dictionary, or if you have legal term suggestion, we'd love to hear from you!