tonometer

n. [ Gr. &unr_; a stretching, a tone + -meter. ] 1. (Physics.) An instrument for determining the rate of vibrations in tones. [ 1913 Webster ]

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. [ 1913 Webster ]