The Collaborative International Dictionary of English v.0.48:

cattail \cat"tail\, Cat-tail \Cat"-tail\(k[a^]t"t[=a]l), n.
   (Bot.)
   A tall erect rush or flag (Typha latifolia) growing widely
   in fresh and salt marshes, with long, flat, sword-shaped
   leaves, having clusters of small brown flowers in a dense
   cylindrical spike at the top of the stem; -- called also
   bulrush and reed mace. The leaves are frequently used for
   seating chairs, making mats, etc. See Catkin.
   [1913 Webster + WordNet 1.5]

   Note: The lesser cat-tail is Typha angustifolia.
         [1913 Webster]

WordNet (r) 3.0 (2006):

cattail
    n 1: tall erect herbs with sword-shaped leaves; cosmopolitan in
         fresh and salt marshes