The Collaborative International Dictionary of English v.0.48:

Yucca \Yuc"ca\, n. [NL., from Yuca, its name in St. Domingo.]
   (Bot.)
   A genus of American liliaceous, sometimes arborescent, plants
   having long, pointed, and often rigid, leaves at the top of a
   more or less woody stem, and bearing a large panicle of showy
   white blossoms.
   [1913 Webster]

   Note: The species with more rigid leaves (as Yucca
         aloifolia, Yucca Treculiana, and Yucca baccata)
         are called Spanish bayonet, and one with softer
         leaves (Yucca filamentosa) is called bear grass,
         and Adam's needle.
         [1913 Webster]

   Yucca moth (Zool.), a small silvery moth (Pronuba
      yuccasella) whose larvae feed on plants of the genus
      Yucca.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Yucca aloifolia
    n 1: a stiff yucca with a short trunk; found in the southern
         United States and tropical America; has rigid spine-tipped
         leaves and clusters of white flowers [syn: Spanish
         bayonet, Yucca aloifolia]