The Collaborative International Dictionary of English v.0.48:

Longbow \Long"bow`\, n.
   The ordinary bow, not mounted on a stock; -- so called in
   distinction from the crossbow when both were used as
   weapons of war. Also, sometimes, such a bow of about the
   height of a man, as distinguished from a much shorter one.
   [1913 Webster]

   To draw the longbow, to tell large stories.
      [1913 Webster]

WordNet (r) 3.0 (2006):

longbow
    n 1: a powerful wooden bow drawn by hand; usually 5-6 feet long;
         used in medieval England