The Collaborative International Dictionary of English v.0.48:

Bulrush \Bul"rush`\ (b[.u]l"r[u^]sh`), n. [OE. bulrysche,
   bolroysche; of uncertain origin, perh. fr. bole stem + rush.]
   (Bot.)
   A kind of large rush, growing in wet land or in water.
   [1913 Webster]

   Note: The name bulrush is applied in England especially to
         the cat-tail (Typha latifolia and Typha
         angustifolia) and to the lake club-rush (Scirpus
         lacustris); in America, to the Juncus effusus, and
         also to species of Scirpus or club-rush.
         [1913 Webster]

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):

bulrush
    n 1: tall marsh plant with cylindrical seed heads that explode
         when mature shedding large quantities of down; its long
         flat leaves are used for making mats and chair seats; of
         North America, Europe, Asia and North Africa [syn:
         cat's-tail, bullrush, bulrush, nailrod, reed
         mace, reedmace, Typha latifolia]
    2: tall rush with soft erect or arching stems found in Eurasia,
       Australia, New Zealand, and common in North America [syn:
       bulrush, bullrush, common rush, soft rush, Juncus
       effusus]