Source : Webster's Revised Unabridged Dictionary (1913)

Microcoustic \Mi`cro*cous"tic\, a. [Micro- + acoustic: cf. F.
   microcoustique, micracoustique.]
   Pertaining, or suited, to the audition of small sounds;
   fitted to assist hearing.

Microcoustic \Mi`cro*cous"tic\, n.
   An instrument for making faint sounds audible, as to a
   partially deaf person.