mangabeyPronunciation: /ˈmaŋgəbeɪ/Definition of mangabey noun a medium-sized long-tailed monkey native to the forests of West and central Africa. Genus Cercocebus, family Cercopithecidae: several species Origin: late 18th century: by erroneous association with Mangabey, a region of Madagascarmangabey in other Oxford dictionaries Definition of mangabey in the US English dictionary