Green’s Dictionary of Slang

one who sings, plays or otherwise entertains in public houses or, latterly, on the street, typically alongside a cinema queue.

1855		Yokel’s Preceptor 29: Buskers, Itinerant vocalists, or spouters.
1860		Hotten Dict. of Modern Sl. etc. 14: BUSKER, a man who sings or performs in a public house.
1889		Clarkson & Richardson Police! 237: He is known as the ‘Irish busker’ [...] In ‘flash’ language, the resorts are described, not as lodging houses, but [...] ‘dossing cribs,’ ‘snoozing jugs,’ ‘cadgers’ covers,’ ‘tourist cabins,’ and ‘buskers’ retreats.’.
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 22: BUSK, BUSKING: [...] street instrumentalists or vocalists are called buskers – the profession busking.
1906		O.C. Malvery Soul Market 37: It was Nellie who gave [...] me an informal introduction to a company of ‘buskers’.
1911		G.R. Sims Off the Track in London 170: The rough, boisterous sailor-folk are simply having ‘fun’ with the Scotch ‘busker’.
1937		J. Worby Other Half 161: I’m a busker. I chant in the streets.
1941		V. Davis Phenomena in Crime 34: He was a friend to all beggars, buskers and impecunious crooks.
1976		(con. 1950s) J. Wolveridge Ain’t it Grand 92: We were up in Montmartre and there were three buskers.
1995		(con. 1860s) P. Ackroyd Dan Leno and the Limehouse Golem 102: He started as a busker.