bullpen vs prison cell

bullpen and prison cell both are nouns.

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

As nouns, prison cell is a hypernym of bullpen; that is, prison 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
prison cell: a room where a prisoner is kept

Other hypernyms of bullpen include cell, jail cell.

bullpen (noun)	prison 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