The Collaborative International Dictionary of English v.0.48:

Oleander \O`le*an"der\, n. [F. ol['e]andre (cf. It. oleandro,
   LL. lorandrum), prob. corrupted, under the influence of
   laurus laurel, fr. L. rhododendron, Gr. ?; ? rose + ? tree.]
   (Bot.)
   A beautiful evergreen shrub (Nerium oleander) of the
   Dogbane family, having clusters of fragrant red, white, or
   pink flowers. It is a native of the East Indies, but the red
   variety has become common in the south of Europe. Called also
   rosebay, rose laurel, and South-sea rose.
   [1913 Webster +PJC]

   Note: Every part of the plant is dangerously poisonous, and
         death has occured from using its wood for skewers in
         cooking meat.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rosebay \Rose"bay`\, n. (Bot.)
      (a) the oleander. [Obs.]
      (b) Any shrub of the genus Rhododendron. [U.S.]
      (c) An herb (Epilobium spicatum) with showy purple
          flowers, common in Europe and North America; -- called
          also great willow herb.
          [1913 Webster]

WordNet (r) 3.0 (2006):

rosebay
    n 1: late-spring-blooming rhododendron of eastern North America
         having rosy to pink-purple flowers [syn: rosebay,
         Rhododendron maxima]