Nipple confusion: A problem that may beset a bottlefed baby in which it forgets how to nurse on mother's nipple. Breastfeeding requires far more vigorous mouth and tongue motions and greater muscle coordination than bottlefeeding. On bottle nipples or even pacifiers, a newborn can forget how to nurse properly. This confusion can lead to diminished or discontinued nursing. Nipple confusion is usually not a concern after the early weeks, once the baby is nursing well.