E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Slang; dog, or dogs Latin; gibberish.
What did actually reach his ears was disguised so completely by the use of cant words and the thieves Latin, called slang, that he could make no sense of the conversation.Sir W. Scott: Redgauntlet, chap. xiii.
He can vent Greek and Hebrew as fast as I can thieves Latin.Sir W. Scott: Kenilworth, chap. xxix.