A whining manner of speech; class phraseology, especially of a religious nature (Latin, canto, to sing, whence chant). It is often derived from a proper name. We are told that Alexander and Andrew Cant maintained that all those who refused the “Covenant” ought to be excommunicated, and that those were cursed who made use of the prayer-book. These same Cants, in their grace before meat, used to “pray for all those who suffered persecution for their religious opinions.” (Mercurius Publicus, No. ix., 1661.)
The proper name cannot have given us the noun and verb, as they were in familiar use certainly in the time of Ben Jonson, signifying “professional slang,” and “to use professional slang.”
The doctor here, When he discourses of dissection, Of vena cava and of vena porta ... What does he do but cant? Or if he run To his judicial astrology, And trowl out the trine, the quartile, and thesextile, Does he not cant?
Ben Jonson (1574-1637): Andrew Cant died 1664.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894