[acous.tic] or acous.ti.cal adj [Gk akoustikos of hearing, fr. akouein to hear--more at hear] (1605) 1: of or relating to the sense or organs of hearing, to sound, or to the science of sounds "~ apparatus of the ear" "~ energy": as a: deadening or absorbing sound "~ tile" b: operated by or utilizing sound waves
2: of, relating to, or being a musical instrument whose sound is not electronically modified -- acous.ti.cal.ly adv