Old cocoyam: Colocasia esculenta; taro.
New cocoyam: Xanthosoma, particularly Xanthosoma sagittifolium, or the edible root of that plant; malanga.
Any of several other species with similar corms and growth habit in Colocasia, Alocasia etc.
Food from a taro plant.
Colocasia esculenta, raised as a food primarily for its corm, which distantly resembles potato.