Shotgun marriage

A shotgun marriage is when two people who were not planning to get married decide to get married anyway because they have done something that can only be fixed by getting married. For example, if a girl and a boy have a baby together, they might decide to get married even if they weren't planning on it just so they can be a family and raise the baby together. It gets its name because in the old days, if a girl and a boy did something like that, the girl's father would threaten the boy with a shotgun until he agreed to marry his daughter.