Green’s Dictionary of Slang

1. (Aus./Irish) to steal cattle; thus moonlighting n.

1914		Sport (Adelaide) 3 July 4/7: Kadina chaps come to Wallaroo fishing — not to see if they can do moonlighting .
1955		N. Pulliam I Travelled a Lonely Land (1957) 236/1: moonlighting – riding out to hunt sheep or cattle at night.
1966		P.J. Flanagan Cavan and Leitrim Railway 12: Despite the forthright condemnation of the priests a ‘Captain Moonlight’ roamed the Leitrim hills and ‘moonlighting’ became a common pastime .

2. (UK Und.) to engage in criminal activity at night.

1942		Berrey & Van den Bark Amer. Thes. Sl.
1949		Monteleone Criminal Sl. (rev. edn).

3. (orig. US) to work at two jobs in order to boost one’s income. The second job is usu. night work, and the other employer may not know about it; thus more usu. as the n. moonlighting

1970		E. Tidyman Shaft 35: Cops were moonlighting as armed cab drivers.
1978		L. Kramer Faggots 116: He moonlighted, writing twice-monthly features.
1988		D. Woodrell Muscle for the Wing 73: I hear he moonlighted as a collector for a loan shark.
1991		C. Fletcher Pure Cop 109: We get a lot of medical students. They moonlight as pimps and male prostitutes.
1999		Guardian G2 22 July 7: Must he moonlight as a columnist?
2005		K. Huff A Steady Rain I iii: He’d stay out late and tell Connie he was moonlighting.
2009		L. McIlvanney All the Colours 117: ‘They were over here building chapels and they did this place on the side. Moonlighting’.
2011		G. Hayward Corruption Officer [ebk] cap. 22: I moonlight on my days off doing unauthorized security at the local clothing stores.
2013		K. Sampson Killing Pool 216: He’s moonlighting [...] for a few dollars more.