Matrimonial means relating to marriage. When a couple exchanges matrimonial vows at their wedding, they're making the promises that will bind them together as a married couple. A matrimonial ceremony is the formal event where two people get married.

Today we use matrimonial to describe anything connected to the institution or state of marriage itself.

You might encounter this word in formal or legal contexts. A lawyer who specializes in matrimonial law helps people with issues like divorce or custody arrangements. A newspaper's matrimonial ads (common in some countries) are where people advertise that they're looking for someone to marry.

The word carries a more formal, official tone than simply saying “wedding” or “marriage.” Someone might refer to their matrimonial home, meaning the house they share with their spouse. While we have many casual words for marriage and weddings, matrimonial emphasizes the legal and social institution itself.