shamrock pea vs herb

shamrock pea and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
shamrock pea	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hypernym of shamrock pea; that is, herb is a word with a broader meaning than shamrock pea:

shamrock pea: trailing trifoliate Asiatic and African herb having cobalt blue flowers
herb: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

Other hypernyms of shamrock pea include herbaceous plant.

shamrock pea (noun)	herb (noun)
trailing trifoliate Asiatic and African herb having cobalt blue flowers	aromatic potherb used in cookery for its savory qualities
	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests