sweet unicorn plant vs herb

sweet unicorn plant and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet unicorn plant	Yes	No	No	No
herb	Yes	No	No	No

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

sweet unicorn plant: a herbaceous plant of the genus Proboscidea
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 sweet unicorn plant include herbaceous plant.

sweet unicorn plant (noun)	herb (noun)
a herbaceous plant of the genus Proboscidea	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