To cant is, supposedly, to talk sanctimoniously. I've never seen the word in the wild, but I doubt this is its core meaning. It sounds to me musical, and a little looking reveals that it springs from the the Latin for sing, canere, to which we also owe canary and chant. It's easy to imagine how the modern (though seldom seen) meaning crept into place. As the language changes and we don't find ourselves needed to discuss Latin singing the musical connection fades but the ecclesiastical atmosphere remains. Though it left behind one cousin which holds onto the original meaning. Canticle, a word whose apparent dignity is in exact opposition to its actual meaning which is 'little song.'