Moan is also a verb, so whenever someone is hurting enough — physically or mentally — there's the possibility they'll moan in despair or discomfort. You can also use this word to mean "whine" or "complain," like when your little sister moans about how much smaller her slice of pie is than yours. Experts think moan is related to the Old English word mænan, "complain or moan," but that it's also imitative — resembling the sound it describes.