trefoil vs herb

trefoil and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
trefoil	Yes	No	No	No
herb	Yes	No	No	No

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

trefoil: a plant of the genus Trifolium
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 trefoil include herbaceous plant.

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

trefoil: any of several Old World herbs of the genus Medicago having small flowers and trifoliate compound leaves
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 trefoil include herbaceous plant.

trefoil (noun)	herb (noun)
an architectural ornament in the form of three arcs arranged in a circle	aromatic potherb used in cookery for its savory qualities
a plant of the genus Trifolium	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests
any of several Old World herbs of the genus Medicago having small flowers and trifoliate compound leaves