sumo Syllabification: (su·mo)Pronunciation: /ˈso͞omō/Definition of sumo noun (plural sumos) a Japanese form of heavyweight wrestling, in which a wrestler wins a bout by forcing his opponent outside a marked circle or by making him touch the ground with any part of his body except the soles of his feet. a sumo wrestler. Origin:from Japanese sūmosumo in other Oxford dictionaries Definition of sumo in the British & World English dictionary