The Collaborative International Dictionary of English v.0.48:

Rorqual \Ror"qual\, n. [Norw. rorqualus a whale with folds.]
   (Zool.)
   A very large North Atlantic whalebone whale (Physalus
   antiquorum, or Balaenoptera physalus). It has a dorsal
   fin, and strong longitudinal folds on the throat and belly.
   Called also razorback.
   [1913 Webster]

   Note: It is one of the largest of the whales, somethimes
         becoming nearly one hundred feet long, but it is more
         slender than the right whales, and is noted for its
         swiftness. The name is sometimes applied to other
         related species of finback whales.
         [1913 Webster]

WordNet (r) 3.0 (2006):

rorqual
    n 1: any of several baleen whales of the family Balaenopteridae
         having longitudinal grooves on the throat and a small
         pointed dorsal fin [syn: rorqual, razorback]