Pap is any semi-liquid food, such as bread soaked in milk or even the namebrand Pablum, that infants employ to reduce the coefficient of friction that obtains between their palms and the surface of their highchairs. The word apparently originated in the early fifteenth century as a representation of the sound babies make when they are nursing their mothers’ breasts. The other pap—the one meaning breast that appeared in the thirteenth century—likely arose in the same way, as did the much older Latin word pabulum, meaning nourishment.