The Collaborative International Dictionary of English v.0.48:
Humpback \Hump"back`\, n. [Cf. Hunchback.]
1. A crooked back; a humped back. --Tatler.
2. A humpbacked person; a hunchback.
(a) Any whale of the genus Megaptera, characterized by a
hump or bunch on the back. Several species are known.
The most common ones in the North Atlantic are
Megaptera longimana of Europe, and Megaptera
osphyia of America; that of the California coasts is
(b) A small salmon (Oncorhynchus gorbuscha), of the
northwest coast of America; the humpbacked salmon.