The Collaborative International Dictionary of English v.0.48:

Cordaites \Cordaites\ n.
   a genus of tall Paleozoic trees superficially resembling
   modern screw pines; they were structurally intermediate in
   some ways between cycads and conifers.

   Syn: genus Cordaites.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Cordaites
    n 1: tall Paleozoic trees superficially resembling modern screw
         pines; structurally intermediate in some ways between
         cycads and conifers [syn: Cordaites, genus Cordaites]