ground ball vs hopper

ground ball and hopper both are nouns.

Word	Noun	Adjective	Verb	Adverb
ground ball	Yes	No	No	No
hopper	Yes	No	No	No

As nouns, ground ball and hopper are synonyms defined as:

Other synonyms of ground ball include groundball, grounder.

ground ball (noun)	hopper (noun)
(baseball) a hit that travels along the ground	(baseball) a hit that travels along the ground
	terrestrial plant-eating insect with hind legs adapted for leaping
	funnel-shaped receptacle; contents pass by gravity into a receptacle below
	a machine used for picking hops
	someone who hops