The Collaborative International Dictionary of English v.0.48:

Snowdrop \Snow"drop`\, n. (Bot.)
   A bulbous plant (Galanthus nivalis) bearing white flowers,
   which often appear while the snow is on the ground. It is
   cultivated in gardens for its beauty.
   [1913 Webster]

   Snowdrop tree. See Silver-bell tree, under Silver, a.
      [1913 Webster]

WordNet (r) 3.0 (2006):

snowdrop tree
    n 1: medium-sized tree of West Virginia to Florida and Texas
         [syn: silver-bell tree, silverbell tree, snowdrop
         tree, opossum wood, Halesia carolina, Halesia
         tetraptera]