The Collaborative International Dictionary of English v.0.48:

club moss \club" moss`\, clubmoss \clubmoss\n. (Bot.)
   a primitive evergreen mosslike plant with spores in
   club-shaped strobiles, much used in winter decoration. The
   best known species is Lycopodium clavatum, but other
   Lycopodia are often called by this name. The spores form a
   highly inflammable powder.

   Syn: club moss, lycopod.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

club-moss
    n 1: primitive evergreen moss-like plant with spores in club-
         shaped strobiles [syn: club moss, club-moss, lycopod]