cocoyam

coco +‎ yam, because old cocoyam was planted in coconut groves and resembled yams. New cocoyam was so named because it resembled old cocoyam.

cocoyam (plural cocoyams)

1. New cocoyam: Xanthosoma, particularly Xanthosoma sagittifolium, or the edible root of that plant; malanga.
   • 2007 March 30, “Street Level”, in Chicago Reader‎:

     Ampesi, intensely flavored stews or soups, are eaten with fufu, a firm, starchy dumpling made from plantains or cocoyam.

2. Old cocoyam: Colocasia esculenta; taro.

• (new cocoyam): yautia, new cocoyam, otoe, otoy, macabo, malanga, quequisque
• (old cocyam): taro, dasheen
• (to be sorted): tanier, tannia, tannier, taioba