Otacoustic /(ŏt`ȧ*kous"tĭk [or] ō`tȧ-)/

Ot·a·cous·tic

Otacoustic

a.
  1. Assisting the sense of hearing; as, an otacoustic instrument.

Otacoustic

n.
  1. An instrument to facilitate hearing, as an ear trumpet.