WordNet sense 1 (an abnormal backward curve to the vertebral column):

hunchback, kyphosis

WordNet sense 2 (a person whose back is hunched because of abnormal curvature of the upper spine):

crookback

WordNet sense 3 (large whalebone whale with long flippers noted for arching or humping its back as it dives):

humpback whale, Megaptera novaeangliae