bird's foot trefoil vs herb

bird's foot trefoil and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
bird's foot trefoil	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hypernym of bird's foot trefoil; that is, herb is a word with a broader meaning than bird's foot trefoil:

bird's foot trefoil: Old World herb related to fenugreek
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 bird's foot trefoil include herbaceous plant.

bird's foot trefoil (noun)	herb (noun)
European forage plant having claw-shaped pods introduced in America	aromatic potherb used in cookery for its savory qualities
Old World herb related to fenugreek	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests