To retreat, to back down. This expression, which dates back at least to the mid-fourteenth century, refers to the practice of snails, which can withdraw the soft, projecting parts of their body inside their shell when they feel threatened. The snail has no genuine horns. Rather, the front end of its muscular foot has sensory tentacles that look a little like horns, whence the expression. About 1350 an unknown chronicler wrote about Richard the Lionhearted in a particular campaign, “They . . . gunne to drawen in their hornes as a snayle among the thornes.” It has been a cliché since about 1800.