buckeyePronunciation: /ˈbʌkʌɪ/Definition of buckeye noun 1an American tree or shrub related to the horse chestnut, with showy red or white flowers. Genus Aesculus, family Hippocastanaceae: several species the nut of the buckeye. 2 (also buckeye butterfly) an orange and brown New World butterfly with conspicuous eyespots on the wings. Junonia coenia, subfamily Nymphalinae, family Nymphalidae 3 (Buckeye) US informal a native of the state of Ohio. 4 (also buckeye coupling) a kind of automatic coupling for railway rolling stock. [named after the Buckeye Steel Castings Company, Columbus, Ohio]buckeye in other Oxford dictionaries Definition of buckeye in the US English dictionary