crimson clover vs trefoil

crimson clover and trefoil both are nouns.

Word	Noun	Adjective	Verb	Adverb
crimson clover	Yes	No	No	No
trefoil	Yes	No	No	No

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

crimson clover: southern European annual with spiky heads of crimson flower; extensively cultivated in United States for forage
trefoil: a plant of the genus Trifolium

Other hypernyms of crimson clover include clover.

crimson clover (noun)	trefoil (noun)
southern European annual with spiky heads of crimson flower; extensively cultivated in United States for forage	an architectural ornament in the form of three arcs arranged in a circle
	a plant of the genus Trifolium
	any of several Old World herbs of the genus Medicago having small flowers and trifoliate compound leaves