bullpen vs jail cell

bullpen and jail cell both are nouns.

Word	Noun	Adjective	Verb	Adverb
bullpen	Yes	No	No	No
jail cell	Yes	No	No	No

As nouns, jail cell is a hypernym of bullpen; that is, jail cell is a word with a broader meaning than bullpen:

bullpen: a large cell where prisoners (people awaiting trial or sentence or refugees or illegal immigrants) are confined together temporarily
jail cell: a room where a prisoner is kept

Other hypernyms of bullpen include cell, prison cell.

bullpen (noun)	jail cell (noun)
a large cell where prisoners (people awaiting trial or sentence or refugees or illegal immigrants) are confined together temporarily	a room where a prisoner is kept
a place on a baseball field where relief pitchers can warm up during a game