trefoil vs red clover

trefoil and red clover both are nouns.

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

As nouns, red clover is a hyponym of trefoil; that is, red clover is a word with a more specific, narrower meaning than trefoil:

trefoil: a plant of the genus Trifolium
red clover: erect to decumbent short-lived perennial having red-purple to pink flowers; the most commonly grown forage clover

trefoil (noun)	red clover (noun)
an architectural ornament in the form of three arcs arranged in a circle	erect to decumbent short-lived perennial having red-purple to pink flowers; the most commonly grown forage clover
a plant of the genus Trifolium
any of several Old World herbs of the genus Medicago having small flowers and trifoliate compound leaves