Close, intimate, side by side. The term is a very old one, dating back to the sixteenth century (when it apparently replaced the still older cheek by cheek: “I’ll go with thee, cheek by jowl,” wrote Shakespeare in A Midsummer Night’s Dream, 3.2). Eric Partridge deemed it a cliché by the mid-eighteenth century.

To speak ironically or mockingly; slyly insincere. Presumably this term originally referred to the mocking facial expression resulting from poking one’s tongue in one’s cheek. It dates from the first half of the nineteenth century. H. McLeave used it in Borderline Case (1979): “‘Only for those people who have something sinister to hide,’ he said, tongue-in-cheek.”

To respond meekly to insults, provocation, or oppression. The term comes from the Bible, where Jesus exhorts his followers, “Unto him that smiteth thee on the one cheek offer also the other” (Luke 6:29). Although the term persists to the present, over the centuries it has given rise to heated arguments concerning the wisdom of such behavior. “Turning the other cheek is a kind of moral jiu-jitsu,” wrote Gerald S. Lee in Crowds (1913), but some psychologists believe it simply encourages the aggressor and heightens hostilities.