旧 former

一 (one/line radical) + 日 (sun, day)

★☆☆☆☆

5 strokes

PREFIX meaning 'former.' It can be used with lots of different words, but unfortunately none of them are really super-handy. For example . . .

Onyomi

KYUU	One day I will re-unite with my CUTE former girlfriend.

旧姓(きゅうせい)	maiden name ★☆☆☆☆ 旧 (former) + 姓 (family name) = 旧姓 (maiden name)
復旧する(ふっきゅうする)	to resume service ☆☆☆☆☆ 復 (return or re-do) + 旧 (former) = 復旧する (to resume service)