Merriam-Webster Collegiate Dictionary - periwinkle

 I. noun  Etymology: Middle English perwinke, from Old English perwince, from Vulgar Latin *pervinca, short for Latin vincapervinca  Date: before 12th century  1. any of several trailing or woody evergreen herbs of the dogbane family: as  a.  (1) a European creeper (Vinca minor) widely cultivated as a ground cover and for its blue or white flowers — called also myrtle  (2) a trailing plant (Vinca major) with large blue flowers that is used as a ground cover and in window boxes  b. rosy ~  2. a light purplish blue — called also ~ blue  II. noun  Etymology: Middle English *~, alteration of Old English pinewincle, from Latin pina, a kind of mussel (from Greek) + Old English -wincle (akin to Danish vincle snail shell)  Date: circa 1530 any of various gastropod mollusks: as  a. any of a genus (Littorina) of edible littoral marine snails; also any of various similar or related marine snails  b. any of several North American freshwater snails