The Collaborative International Dictionary of English v.0.48:

Alcyonium \Al`cy*o"ni*um\, n. [Gr. ? a zo["o]phyte, so called
   from being like the halcyon's nest.] (Zool.)
   A genus of fleshy Alcyonaria, its polyps somewhat resembling
   flowers with eight fringed rays. The term was also formerly
   used for certain species of sponges.
   [1913 Webster]