Green’s Dictionary of Slang

(UK Und.) a thief who crawls over house-tops and breaks in through garret windows.

1864, 1867, 1870		Hotten Sl. Dict. 141: garreter a thief who crawls over the tops of houses, and enters garret-windows.
1869		Australiasian (Melbourne) 17 July 8/5: A man who gets over roofs or in at windows is called a garreter and a dancer.
1873		Sl. Dict.
1889		Clarkson & Richardson Police! 260: About 40 were burglars, ‘dancers,’ ‘garreters,’ and others adept with the skeleton keys.
1890–1904		Farmer & Henley Sl. and Its Analogues III 120/2: Garreteer subs. (thieves’) A thief whose speciality is to rob houses by entering sky-lights or garret-windows.
1895		Crowe Aus. Sl. Dict. 31: Garreter, a thief who robs by getting through the upper window.