Tongue and Cheek
To say something "tongue-in-cheek" is to say it in an ironic, kidding or nonserious way. A nonliteral way, even. It is commonly believed that the saying is derived from the 18th-century practice of actually placing one's tongue against the inside of one's cheek after saying something to show that it's intended as a joke [source: Education Bug]. The phrase "tongue-and-cheek," therefore, doesn't make sense, despite its wide use among those unfamiliar with the origin of the appropriate phrase [source: Grammarist].