An event or document which pre-dates a marriage.
For example, an "antenuptial agreement" is one which is signed before marriage.
A antenuptial gift is a gift given by one spouse to the other before marriage.
In
"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."