pp. Doing paid work while taking time away from one's day job.
Allowing an employee to reconfigure her day can lead to free agency. First, she takes work home and leaves early on certain afternoons. Then she arranges to telecommute three days per week. Then, while she's telecommuting, she begins moonlighting — or "sunlighting." if she's working on side gigs during the day.
—Daniel Pink, Free Agent Nation, Warner Books, April 01, 2001
1983 (earliest)
In Spain the title of civil servant has long been a misnomer. They are civil enough. But they rarely serve. Bureaucrats practiced moonlighting to such an extent it turned into sunlighting. It was not unusual for them to hold down two, sometimes three — and in one case, a reliable source swears, four — separate jobs.
—John Darnton, “Madrid's new working class: the bureaucrats,” The New York Times, February 07, 1983
This word is a play on moonlighting — "doing paid work in the evening or at night in addition to one's day job" — which has been in the language since 1957. The Oxford English Dictionary has an entry for sunlighting, which would normally disqualify it as a Word Spy term. However, sunlighting seems to have become quite popular over the past few years (I found half a dozen citations since 2000), so I'm declaring it post-worthy. The OED's two earliest citations are from medical journals — one in 1977 and one in 1978.