ribgrass vs buckthorn

ribgrass and buckthorn both are nouns.

Word	Noun	Adjective	Verb	Adverb
ribgrass	Yes	No	No	No
buckthorn	Yes	No	No	No

As nouns, ribgrass and buckthorn are synonyms defined as:

ribgrass and buckthorn: an Old World plantain with long narrow ribbed leaves widely established in temperate regions

ribgrass (noun)	buckthorn (noun)
an Old World plantain with long narrow ribbed leaves widely established in temperate regions	any shrub or small tree of the genus Bumelia
	a shrub or shrubby tree of the genus Rhamnus; fruits are source of yellow dyes or pigments
	an Old World plantain with long narrow ribbed leaves widely established in temperate regions