origanum vs herb

origanum and herb both are nouns.

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

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

origanum: any of various fragrant aromatic herbs of the genus Origanum used as seasonings
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 origanum include herbaceous plant.

origanum (noun)	herb (noun)
any of various fragrant aromatic herbs of the genus Origanum used as seasonings	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