aiding hearing
• (n.) Alt. of Otacousticon • (a.) Assisting the sense of hearing; as, an otacoustic instrument.
Ot`a·cous'tic adjective [ Oto- + acoustic : confer French otacoustique .] Assisting the sense of hearing; as, an otacoustic instrument. 
otacoustic, otacoustical, otacousticon 1. Aiding or concerning hearing. 2. A reference to an instrument used to assist hearing; such as, an ear-trumpet.