nestmate in English dictionary nestmate Meanings and definitions of "nestmate" One with which a nest is shared, such as a baby bird and its siblings or figuratively a child with children it is raised with. noun One with which a nest is shared, such as a baby bird and its siblings or figuratively a child with children it is raised with. more Grammar and declension of nestmate nestmate ( plural nestmates) nestmate (plural nestmates) more Sample sentences with "nestmate" Declension Stem Try again Available translations Russian Authors