What does "acoustics" mean?

Acoustics: The science of sounds, teaching their nature, phenomena, and laws. Acoustics, then, or the science of sound, is a very considerable branch of physics. Sir J. Herschel. Note: The science is, by some writers, divided, into diacoustics, which explains the properties of sounds coming directly from the ear; and catacoustica, which treats of reflected sounds or echoes.