What does Reünist mean?

As a reünist she still came back every year for the lustrum trip.

Dutch student slang. This is a Dutch word. You will hear it a lot at Dutch universities, student associations and in student houses.

Reünisten often stay closely involved with their old association or dispuut, long after graduating. They show up at the dies, the lustrum and sometimes with a big donation. Once a member, always a member.