herb vs herbaceous plant

herb and herbaceous plant both are nouns.

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

As nouns, herb and herbaceous plant are synonyms defined as:

herb and herbaceous plant: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

herb (noun)	herbaceous plant (noun)
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
a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests