Source : Webster's Revised Unabridged Dictionary (1913)

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}.