To work on the side (at a secondary job), often in the evening or during the night.
To engage in an activity other than what one is known for.
To perform a secondary function substantially different from its supposed primary function, as in protein moonlighting.
The light reflected from the Moon.
To work a typical job beginning at 9 a.m. and ending at 5 p.m.
Of a job, beginning at 9 a.m. and ending at 5 p.m., the usual office hours in many countries.