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):

bear grass
    n 1: yucca of southern United States having a clump of basal
         grasslike leaves and a central stalk with a terminal raceme
         of small whitish flowers [syn: bear grass, Yucca
         smalliana]
    2: yucca of west central United States having a clump of basal
       grasslike leaves and a central stalk with a terminal raceme
       of small whitish flowers [syn: bear grass, Yucca glauca]
    3: stemless plant with tufts of grasslike leaves and erect
       panicle of minute creamy white flowers; southwestern United
       States and Mexico [syn: bear grass, Nolina microcarpa]
    4: plant of western North America having woody rhizomes and
       tufts of stiff grasslike basal leaves and spikes of creamy
       white flowers [syn: squaw grass, bear grass, Xerophyllum
       tenax]