Cant is language repeated so often and so mechanically that it's essentially empty of meaning. Cant can also mean the specialized jargon of a particular group — like the "cant of piracy" (e.g., Ahoy! Lubber! Arrr!).
Possible sources for cant exist in both Irish Gaelic and Latin, and the meanings of both are similar: caint is "speech," while cantare is "to sing." In broader English, the word was first used to mock the singing of monks. As it evolved, cant became the whining of beggars and then the secret language of thieves, and the negative connotations persist in modern usage. As a verb, cant has a completely different meaning: it means to lean or tilt to one side.