Preaching with a whining, affected tone, perhaps a corruption of chaunting; some derive it from Andrew Cant, a famous Scotch preacher, who used that whining manner of expression. Also a kind of gibberish used by thieves and gypsies, called likewise pedlar’s French, the slang, &c. &c.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1736 dictionary of canting and thieving slang.
Canticle * CantersNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes