Green’s Dictionary of Slang

a professional thief or criminal mendicant; one who speaks the thieves’ language.

c.1605		Middleton More Dissemblers Besides Women IV ii: O dainty fine doxy! She speaks the language as familiarly already as if she’d been begot of a canter.
1615		T. Overbury New and Choise Characters n.p.: [An Hypocrite] Like Canters & Gypsies: they are all zeale, no knowledge.
1626		Jonson Staple of News II i: A rogue, A very canter, I, sir, one that maunds Upon the pad.
1654		Witts Recreations ‘Fancies & Fantasticks’ No. 124: From Canters and great eaters [...] Heaven deliver me.
c.1661		A Beggar I’ll Be in Farmer Musa Pedestris (1896) 26: A Craver my Father, a Maunder my Mother, / A Filer my Sister, a Filcher my Brother, / A Canter my Unkle, that car’d not for Pelf, / A Litter my Aunt, and a Beggar my self.
1707		J. Shirley Triumph of Wit 182: The Canters have their several Offices or Degrees amongst them.
1719		in D’Urfey Pills to Purge Melancholy III 100: [as cit. c.1661].
1754		‘The Beggar’ Muses Delight 133: [as cit. c.1661].
1785		Grose Classical Dict. of the Vulgar Tongue n.p.: The canters have, it seems a tradition, that from the three first articles of this oath, the first founders of a certain boastful, worshipful fraternity (who pretend to derive their origin from the earliest times) borrowed both the hint and form of their establishment.
1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn) n.p.: Canters, or The Canting Crew. Thieves, beggars, and gypsies, or any others using the canting lingo.
1811		Lex. Balatronicum [as cit. 1796].
1922		Joyce Ulysses 319: We know those canters, says he, preaching and picking your pocket.