[Greek akoustikos, from akouein, to hear (acou- comes from the latter).]

Acoustics is the branch of physics concerned with the properties of sound; the field of acoustooptics studies interactions between very high frequency sound waves and beams of laser light. In medicine, acousma (also called acouasm) is a non-verbal auditory hallucination, such as a ringing or hissing; acousticophobia is fear of noise. See also -acusis and audio-.