fly ball vs liner

fly ball and liner both are nouns.

Word	Noun	Adjective	Verb	Adverb
fly ball	Yes	No	No	No
liner	Yes	No	No	No

As nouns, liner is a hyponym of fly ball; that is, liner is a word with a more specific, narrower meaning than fly ball:

Other hyponyms of fly ball include blast, pop-fly, pop-up, pop fly, line drive, flare, Texas leaguer.

fly ball (noun)	liner (noun)
(baseball) a hit that flies up in the air	(baseball) a hit that flies straight out from the batter
	a large commercial ship (especially one that carries passengers on a regular schedule)
	a piece of cloth that is used as the inside surface of a garment
	a protective covering that protects an inside surface