Finback \Fin"back`\, n. (Zo["o]l.) Any whale of the genera Sibbaldius, Bal[ae]noptera, and allied genera, of the family Bal[ae]nopterid[ae], characterized by a prominent fin on the back. The common finbacks of the New England coast are Sibbaldius tectirostris and S. tuberosus.

Source: Webster's Revised Unabridged Dictionary (1913)