The Collaborative International Dictionary of English v.0.48:

Jonah \Jo"nah\, n.
   The Hebrew prophet, who was cast overboard as one who
   endangered the ship; hence, any person whose presence is
   unpropitious.
   [1913 Webster]

   Jonah crab (Zool.), a large crab (Cancer borealis) of the
      eastern coast of the United States, sometimes found
      between tides, but usually in deep water.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Jonah
    n 1: (Old Testament) Jonah did not wish to become a prophet so
         God caused a great storm to throw him overboard from a
         ship; he was saved by being swallowed by a whale that
         vomited him out onto dry land
    2: a person believed to bring bad luck to those around him [syn:
       jonah, jinx]
    3: a book in the Old Testament that tells the story of Jonah and
       the whale [syn: Jonah, Book of Jonah]