leguminous plant vs herb

leguminous plant and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
leguminous plant	Yes	No	No	No
herb	Yes	No	No	No

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

leguminous plant: an erect or climbing bean or pea plant of the family Leguminosae
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 leguminous plant include herbaceous plant, climber.

leguminous plant (noun)	herb (noun)
an erect or climbing bean or pea plant of the family Leguminosae	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