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 baccata
    n 1: tall yucca of the southwestern United States and Mexico
         having a woody stem and stiff swordlike pointed leaves and
         a large cluster of white flowers [syn: Spanish bayonet,
         Yucca baccata]