› a very young child: Sandra had a baby on May 29th. My younger brother is the baby of the family. › Baby can be used to refer to anything young or smaller than usual: baby corn/lima beans › disapproving Baby can also mean someone who is behaving childishly: She complained like a baby about her boyfriend. › infml Baby is an affectionate way of addressing someone. › infml A baby can also be a project or job someone has a special interest in or responsibility for: The new computer system is really Phil’s baby.