It’s not every modern songwriter whose lyrics allude to fops, mariners and magistrates. Ever rarer is one who seamlessly uses words like “purloined,” “penitent” and “pantaloons” in a song.

But Colin Meloy isn’t much like his musical peers.

“There’s a misconception that I intend to send people to their dictionaries at every opportunity,” says Meloy, 30, with a sigh. “It bums me out that it has become remarkable to use poetic words. A lot of beautiful words are getting lost.”

Meloy isn’t just out to rescue them. He means to make a case for antique terms like “parapets,” “corncobs” and “tamaracks” as part of a fresh and present language.

With his band, the Decemberists, Meloy has seized on some of the imagery, verbiage and musicality of old folk music. But, as Meloy explains, “this isn’t exactly The Chieftains.”

In fact, the Decemberists’ rejiggered approach to folk has made them darlings of the indie-rock set. They’re most frequently compared to Belle & Sebastian, with whom they share an ironic style that, at first, sounds too precious to be believed.

Meloy says he has a surefire method to avoid stuffiness in his music. “(I) use toilet humor,” he says. “It’s the Morrissey approach. He has this brilliant ability to mix a high-minded esthetic with the most sophomoric humor. I don’t think people recognize how viciously funny he is because they’ve lost their sense of irony.”

You’ll need a healthy dose of that to appreciate the songs on the Decemberists’ newly released third album, “Picaresque.” Like its predecessors, it’s filled with allusions to rogues and prostitutes, sailors and kings. The music makes use of instruments as obscure as the shofar, the ancient religious horn of Judaism. While Meloy’s beautiful voice and fluid music can seem utterly earnest, the results aren’t so simple.

He developed his fanciful approach to character and language while studying creative writing at the University of Montana. Born in Helena, Mont., Meloy lived in the country and raised horses as a kid. His older sister, Malie Meloy, grew up to be a writer, too. She’s the author of the well-reviewed 2003 novel “Liars and Saints.”