river shad vs shad

river shad and shad both are nouns.

Word	Noun	Adjective	Verb	Adverb
river shad	Yes	No	No	No
shad	Yes	No	No	No

As nouns, shad is a hypernym of river shad; that is, shad is a word with a broader meaning than river shad:

river shad: shad that spawns in streams of the Mississippi drainage; very similar to Alosa sapidissima
shad: herring-like food fishes that migrate from the sea to fresh water to spawn

river shad (noun)	shad (noun)
shad that spawns in streams of the Mississippi drainage; very similar to Alosa sapidissima	herring-like food fishes that migrate from the sea to fresh water to spawn
	bony flesh of herring-like fish usually caught during their migration to fresh water for spawning; especially of Atlantic coast