The word "acoustic" is derived from the Greek word ἀκουστικός (akoustikos), meaning "of or for hearing, ready to hear" fundamentally derived from the verb ἀκούω(akouo), "I hear". Today - the meaning is not constrained by the frequency range of human perception, including vibration in solids, how it relates to airborne sound, underwater acoustics, and both infrasound and ultrasound.
Take a look at the Circle of Acoustics, first conceived by Bruce Lindsay in 1964, showing all acoustic disciplines. It's best explored by zooming in.
Despite being recently updated, the diagram only implys the math and computer science tools required to quantitatively describe sound. In 1964, calculus, information theory, and Fourier theory may have been sufficient - today analyzing acoustic systems and generating acoustic signals often requires finite element methods (or more broadly, computational acoustics), modern signal processing, and statistical approaches, including AI. The field of Human Machine Interaction also relatively new, and belongs with Communication.