clammy chickweed vs herb

clammy chickweed and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
clammy chickweed	Yes	No	No	No
herb	Yes	No	No	No

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

clammy chickweed: any of various plants related to the common chickweed
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 clammy chickweed include herbaceous plant.

clammy chickweed (noun)	herb (noun)
any of various plants related to the common chickweed	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