Source : Webster's Revised Unabridged Dictionary (1913)

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}.

Source : WordNet®

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