moonlight (v.)

"hold a second job, especially at night," 1957 (implied in the verbal noun moonlighting), from moonlighter "one who takes a second job after hours" (1954), from the notion of working by the light of the moon; see moonlight (n.). Earlier the verb had been used to mean "commit crimes at night" (1882), from moonlighter in reference to members of organized bands that carried on agrarian outrages in Ireland. And compare moonshine. Moonlighter in American English meant "one of a party who go about serenading on moonlit nights" (by 1897).

"light of the moon," c. 1300, from moon (n.) + light (n.). Similar formation in Dutch maanlicht, German Mondlicht.