PREFIX meaning 'former.' It can be used with lots of different words, but unfortunately none of them are really super-handy. For example . . .
One day I will re-unite with my CUTE former girlfriend.
旧 (former) + 姓 (family name)
= 旧姓 (maiden name)
to resume service
復 (return or re-do) + 旧 (former)
= 復旧 (to resume service)