The Capitoline Wolf breastfeeding Romulus and Remus.
Breast feeding or nursing was the act of using one's breast to nurse a newborn infant. In Humans, females are geared for nursing the young. (TNG: "The Outcast")
When William Riker was hesitant at eating pagh, it was jokingly suggested that he might as well have one of the Klingon females breast feed him, comparing him to an infant. (TNG: "A Matter Of Honor")
In 2367, Junior was compared to a baby nursing from her mother, in this case, the USS Enterprise. (TNG: "Galaxy's Child")
In 2372, during Jadzia Dax's zhian'tara, Audrid Dax, in the body of Quark, spoke of the joy of holding a baby to one's breast and nursing it. (DS9: "Facets")
In an alternate timeline, shortly after giving birth, Samantha Wildman planned on breast feeding her newborn daughter, Naomi. The Doctor informed her that, since she lacked the scales of Ktarians, she would be unable to breast-feed in three to four weeks when Naomi's incisors erupted. (VOY: "Deadlock")