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Otacoustic \Ot`a*cous"tic\, a. [Oto- + acoustic: cf. F. otacoustique.] Assisting the sense of hearing; as, an otacoustic instrument. Otacoustic \Ot`a*cous"tic\, Otacousticon \Ot`a*cous"ti*con\, n. An instrument to facilitate hearing, as an ear trumpet.