large periwinkle vs periwinkle

large periwinkle and periwinkle both are nouns.

Word	Noun	Adjective	Verb	Adverb
large periwinkle	Yes	No	No	No
periwinkle	Yes	No	No	No

As nouns, periwinkle is a hypernym of large periwinkle; that is, periwinkle is a word with a broader meaning than large periwinkle:

large periwinkle (noun)	periwinkle (noun)
plant having variegated foliage and used for window boxes	edible marine gastropod
	small edible marine snail; steamed in wine or baked
	chiefly trailing poisonous plants with blue flowers
	commonly cultivated Old World woody herb having large pinkish to red flowers