But it was in the eighteenth century that the word dropped the training wheels and really got moving. It was then that the sense of the language or jargon, often secret, of a group became current, as in thieves' cant. From there, it was an easy transition to the language of a profession or a religious sect, as in canting hypocrite.
Well into the eighteenth century, cant came to be understood as set or stock phrases, fashionable cliches, and, the OED says, "phraseology used for fashion's sake rather than genuine sentiment." It was for this sense that Samuel Johnson advised James Boswell, "Clear you mind of cant."
English gets the word from the Latin cantus, singing, song, or chant, from the Latin verb cantare, to sing.
Given the continuing prevalence of jargon, fashionable cliche, empty sentiment, and hypocrisy, it's a handy word to have at the ready.