sweet buckeye vs buckeye

sweet buckeye and buckeye both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet buckeye	Yes	No	No	No
buckeye	Yes	No	No	No

As nouns, buckeye is a hypernym of sweet buckeye; that is, buckeye is a word with a broader meaning than sweet buckeye:

sweet buckeye: a tall and often cultivated buckeye of the central United States
buckeye: tree having palmate leaves and large clusters of white to red flowers followed by brown shiny inedible seeds

Other hypernyms of sweet buckeye include Aesculus hippocastanum, horse chestnut.

sweet buckeye (noun)	buckeye (noun)
a tall and often cultivated buckeye of the central United States	tree having palmate leaves and large clusters of white to red flowers followed by brown shiny inedible seeds
	the inedible nutlike seed of the horse chestnut