Real Dictionary

periwinkle
countable noun: Periwinkles are small sea snails that can be eaten.
variable noun: Periwinkle is a plant that grows along the ground and has blue flowers.

periwinkle in American English 1
any of a genus (Vinca) of trailing or erect, evergreen plants of the dogbane family; esp., a creeper (V. minor) with blue, white, or pink flowers, grown as a ground cover
noun: any of various marine gastropods or sea snails, esp Littorina littorea, used for food in Europe

periwinkle in American English 2
any of a family (Littorinidae) of small, intertidal saltwater snails having a thick, globular shell: some species are edible
noun: a trailing plant, Vinca minor, of the dogbane family, having glossy, evergreen foliage and usually blue-violet flowers

periwinkle in British English 1
noun: any of various edible marine gastropods of the genus Littorina, esp L. littorea, having a spirally coiled shell

periwinkle in British English 2
noun: any of several Eurasian apocynaceous evergreen plants of the genus Vinca, such as V. minor ( lesser periwinkle) and V. major ( greater periwinkle), having trailing stems and blue flowers
noun: any of several Eurasian apocynaceous evergreen plants of the genus Vinca, such as V. minor ( lesser periwinkle) and V. major (greater periwinkle), having trailing stems and blue flowers