sounding board vs doer

sounding board and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
sounding board	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of sounding board; that is, doer is a word with a broader meaning than sounding board:

sounding board: a person whose reactions to something serve as an indication of its acceptability
doer: a person who acts and gets things done

Other hypernyms of sounding board include actor, worker.

sounding board (noun)	doer (noun)
(music) resonator consisting of a thin board whose vibrations reinforce the sound of the instrument	a person who acts and gets things done
a person whose reactions to something serve as an indication of its acceptability