n. The nipple of the mammary gland.n. Some nipple-like or mammillary structure.n. In entomology, a small conical process or appendage on a surface; a mammula.n. [capitalized] In conchology, a genus of gastropods.n. In botany, applied specificallyn. to tubercles on a plant-surface, as in Mamillarian. to the apex of the nucleus of an ovulen. to granular prominences on some pollen-grains.