Reply #36: It's from an old French word.

[Xithras]

Gigole. It basically translated to "dancing girls" (or prostitutes, depending on its use) and in French speaking areas went from a term for the girls, to a term for the places they danced, to a term for dance halls in general. By the time the Jazz musicians picked it up in New Orleans a century ago, the word had been shortened to Gig and meant any place that people danced in...so playing a gig meant you were going to be the band at a dance. Eventually even the dancing part was dropped, so now it's just playing in front of a crowd.

BTW, Gigole is related to both gigolo (originally a dancing boy) and jiggly (to shake). Word etymology is fun :)