Source : Webster's Revised Unabridged Dictionary (1913)

Periwinkle \Per"i*win`kle\, n. [OE. pervenke, AS. pervince, fr.
   L. pervinca.] (Bot.)
   A trailing herb of the genus {Vinca}.

   Note: The common perwinkle ({Vinca minor}) has opposite
         evergreen leaves and solitary blue or white flowers in
         their axils. In America it is often miscalled {myrtle}.
         See under {Myrtle}.

Source : WordNet®

Vinca minor
     n : widely cultivated as a groundcover for its dark green shiny
         leaves and usually blue-violet flowers [syn: {myrtle}]