Supernumerary nipple: An extra nipple. Supernumerary nipples are usually smaller than normal and vestigial (nonfunctional, without accompanying mammary glands). They tend to occur along a roughly curved line that extends from near the armpit, through the center of the normal breast, and down to the lower abdomen. This distribution is very similar to the location of nipples on mammals that have multiple nipples along the underbelly. Supernumerary nipples do not cause problems and do not need to be removed.