• (British) IPA: /əʊtəˈkuːstɪkɒn/

otacousticon (plural otacousticons)

1. (now rare) An instrument to aid hearing, such as an ear trumpet or hearing aid.
   • 1624, Democritus Junior [pseudonym; Robert Burton], The Anatomy of Melancholy: […], 2nd edition, Oxford, Oxfordshire: Printed by John Lichfield and James Short, for Henry Cripps, OCLC 54573970 ↗:

     , New York Review of Books, 2001, p.69:

     […] Gyges' invisible ring, or some rare perspective glass, or otacousticon, which would so multiply species that a man might hear and see all at once […].