The Collaborative International Dictionary of English v.0.48:

Spiderwort \Spi"der*wort`\, n. (Bot.)
   An American endogenous plant (Tradescantia Virginica), with
   long linear leaves and ephemeral blue flowers. The name is
   sometimes extended to other species of the same genus.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spiderwort
    n 1: any plant of the family Commelinaceae [syn: spiderwort,
         dayflower]