viola vs herbaceous plant

viola and herbaceous plant both are nouns.

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

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

viola: any of the numerous plants of the genus Viola
herbaceous plant: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

Other hypernyms of viola include herb.

viola (noun)	herbaceous plant (noun)
any of the numerous plants of the genus Viola	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests
a bowed stringed instrument slightly larger than a violin, tuned a fifth lower