Green’s Dictionary of Slang

1. to speak, esp. to speak tramps’ jargon.

1851		Illus. London News 13 Dec. 35/3: ‘You must know how to rokker (speak) Roumany like your uncle Euri yonder’.
1856		H. Mayhew Great World of London I 6: ‘Can you roker Romany (can you speak cant)?’ one individual ‘on the cross’ will say to another.
1862		Mayhew & Binny Criminal Prisons of London 6: [as cit. 1856].
1876		C. Hindley Life and Adventures of a Cheap Jack 231: Can you rocker Romanie, / Can you patter flash.
1888		J. Runciman Chequers 78: You rakker Rommanis?
1891		F.W. Carew Autobiog. of a Gipsey 107: I goes in and sets myself down and rokkers to him for a couple of hour.
1906		A. McCormick Tinkler-Gypsies of Galloway 258: Can you rokker Romany?
1933		M. Marshall Tramp-Royal on the Toby 2457: Can’t you rokkra Romanes?
1935		X. Petulengro Romany Life 2: Always they rokkered Romany together.
1958		D. Reeve Smoke in the Lanes (Gloss. of Romani terms) 302: rocker – speak, talk.

2. to understand.

1906		E. Pugh Spoilers 251: ‘An’ I must have ’em to go away with. Rokker?’ ‘Yes, Chick.’.
1914		E. Pugh Cockney At Home 135: Young Pridlets he was one o’ them jokers – you rokker the breed – what thinks as inflammation in the nose is funny.