Green’s Dictionary of Slang

bosh n.²

a fiddle .

1846		implied in bosh-faker
1859		Hotten Dict. of Modern Sl. etc. 10: bosh, a fiddle. bosh-faker, a violin player.
1865		Leaves from Diary of Celebrated Burglar 59/2: There stands that black ‘bloke’ Charlie, longing to set his ‘bosh’ a-going.
1876		C. Hindley Life and Adventures of a Cheap Jack 231: Can you rocker Romanie, / Can you fake a bosh?
1887		Cornishman 6 Jan. 4/3: Specimens of mumpers' or tramps' take [...] fake the boshamingy, play the fiddle.
1902		H. Baumann ‘Sl. Ditty’ Londinismen (2nd edn) v: Piratical fakers / Of bosh by the acres.
1906		A. McCormick Tinkler-Gypsies of Galloway 258: Can you kel the bosh?
1927		(con. 1835–40) P. Herring Bold Bendigo 77: ‘What does he mean by fake the bosh?’ Bendigo inquired. ‘It’s flash patter for playing the fiddle. Bosher got his name from fakin’ the bosh.’.

In compounds

bosh-faker (n.) (also bosh-killer, boshman)

a fiddle player.

1846		Swell’s Night Guide 47: A boshman every Tuesday night for hopping and chaunting.
1859		Hotten Dict. of Modern Sl. etc. 10: bosh, a fiddle. bosh-faker, a violin player.
1866		Letters by an Odd Boy 162: Why should I call the violinist who charms my customers a ‘bosh-faker?’.
1873		Sl. Dict. 93: Bosh-Faker a violin player. Term principally used by itinerants.
1893		P.H. Emerson Signor Lippo 42: At half-past ten six of us went out black, the bosh faker, the grid faker, two Joes, Tots and Tarblo.
1935		A.J. Pollock Und. Speaks 11/2: Bosh faker, a violinist.
1984		Partridge DSUE (8th edn) 120/2: from ca. 1850.