hopper vs ground ball

hopper and ground ball both are nouns.

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

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

Other synonyms of hopper include groundball, grounder.

hopper (noun)	ground ball (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