n. [ Phono- + -meter. ] (Physics) An instrument for measuring sounds, as to their intensity, or the frequency of the vibrations. [ 1913 Webster ]
n. [ Photo- + -meter: cf. F. photomètre. ] (Physics) An instrument for measuring the intensity of light, or, more especially, for comparing the relative intensities of different lights, or their relative illuminating power. [ 1913 Webster ]