the broomstitch

The OED citation:

3. colloq. (orig. U.S.). The practice of doing paid work in addition to one's regular employment.
1957 Reporter (N.Y.) 8 Aug. 11/3 He takes two or three hours off and then..departs for a second job... The practice is known as ‘moonlighting’. 1961 Economist 16 Dec. 1145/2 Several attempts have been made to ban moonlighting on the ground that it robs the unemployed of jobs. 1992 N.Y. Times Bk. Rev. 26 July 9/3 They can take long coffee breaks and go on shopping trips during office hours; they have plenty of time for moonlighting.

That earliest citation is indeed younger than either of us.