IPA: /ˈmuːnˌlaɪtə/
KK: /ˈmunˌlaɪtər/
A person who works a second job in addition to their main job, often at night or during their free time.
She is a moonlighter, working as a waitress after her day job as a teacher.
Moonlighter → It is formed from "moon" (from Old English *mōna*, meaning the natural satellite of Earth) and "-lighter" (from the verb "light" meaning to illuminate or provide light). The term "moonlighter" refers to someone who works a second job, often at night, thus metaphorically 'illuminated' by the moon.
Think of someone working at night under the 'moon' — that's why a moonlighter is someone who has a second job during the night.