bedspring vs box spring

bedspring and box spring both are nouns.

Word	Noun	Adjective	Verb	Adverb
bedspring	Yes	No	No	No
box spring	Yes	No	No	No

As nouns, box spring is a hyponym of bedspring; that is, box spring is a word with a more specific, narrower meaning than bedspring:

bedspring: (usually in the plural) one of the springs holding up the mattress of a bed
box spring: a coiled bedspring in a frame that is covered with cloth

bedspring (noun)	box spring (noun)
(usually in the plural) one of the springs holding up the mattress of a bed	a coiled bedspring in a frame that is covered with cloth