The noun wile is good for describing a particular kind of deviousness, but its plural form is most commonly used.
Your charming brother might use his wiles to talk your parents into loaning him money again and again. You can describe your cousin's knack for getting exactly what he wants through slyness and trickery as his wile. Language experts can only guess about the origin of wile, though many believe it's related to the Old Norse vél, or "craft." Others think there may be a connection with the Old English word for "wizard," wicca.