The Collaborative International Dictionary of English v.0.48:

Viscum \Vis"cum\, n. [L.]
   1. (Bot.) A genus of parasitic shrubs, including the
      mistletoe of Europe.
      [1913 Webster]

   2. Birdlime, which is often made from the berries of the
      European mistletoe.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Viscum
    n 1: type genus of the Viscaceae: Old World evergreen shrubs
         parasitic on many trees including oaks but especially apple
         trees, poplars, aspens and cottonwoods [syn: Viscum,
         genus Viscum]