lettuce vs herbaceous plant

lettuce and herbaceous plant both are nouns.

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

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

lettuce: any of various plants of the genus Lactuca
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 lettuce include herb.

lettuce (noun)	herbaceous plant (noun)
leaves of any of various plants of Lactuca sativa	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests
any of various plants of the genus Lactuca
informal terms for money