noun
Etymology: sounding from gerund of sound (IV)
1.
a. : a board or structure placed behind or over a pulpit, rostrum, or platform to give distinctness and sonority to the sound (as voice or music) coming from it — see band shell
b. : a device or agency that gives greater effect (as force, volume, or scope) to or helps propagate opinions or utterances
Congressional hearings provide a sounding board comparable to question time in the House of Commons — Economist
uses the newspapermen merely as a sounding board — Atlantic
2. : soundboard 1
3. : sound boarding