Witch's milk: A folk term for the milk that often comes from the breast of a newborn baby. This temporary phenomenon is due to stimulation of the baby's breasts by the mother's hormones that cross the placenta during pregnancy. The ability of the baby's breasts to respond in this fashion is a mark of baby born at (or near) full-term. The breast of a baby born prematurely cannot enlarge or produce witch's milk (in German, Hexenmilch).
The term "witch's milk" is sometimes applied broadly to milk from the nipple at any time other than during nursing. See also Galactorrhea.