\To*nom"e*ter\, n. [Gr. ? a stretching, a tone +
-meter.]
1. (Physics.) An instrument for determining the rate of
   vibrations in tones.
2. (Physiol.)
   (a) An apparatus for studying and registering the action
       of various fluids and drugs on the excised heart of
       lower animals.
   (b) An instrument for measuring tension, esp. that of the
       eyeball.