Boston rocker vs rocking chair

Boston rocker and rocking chair both are nouns.

Word	Noun	Adjective	Verb	Adverb
Boston rocker	Yes	No	No	No
rocking chair	Yes	No	No	No

As nouns, rocking chair is a hypernym of Boston rocker; that is, rocking chair is a word with a broader meaning than Boston rocker:

Boston rocker: a rocking chair that has a high spindle back and a decorative top panel
rocking chair: a chair mounted on rockers

Other hypernyms of Boston rocker include rocker.

Boston rocker (noun)	rocking chair (noun)
a rocking chair that has a high spindle back and a decorative top panel	a chair mounted on rockers