a·cous·tic / əˈkoōstik/ • adj. 1. relating to sound or the sense of hearing: dogs have a much greater acoustic range than humans. ∎ (of building materials) used for soundproofing or modifying sound: acoustic tiles. ∎ (of an explosive mine or other weapon) able to be set off by sound waves.2. (of music or musical instruments) not having electrical amplification: acoustic guitar.• n. 1. (usu. acoustics) the properties or qualities of a room or building that determine how sound is transmitted in it. ∎ (acoustic) the acoustic properties or ambience of a sound recording or of a recording studio.2. (acoustics) [treated as sing.] the branch of physics concerned with the properties of sound.3. a musical instrument without electrical amplification, typically a guitar.DERIVATIVES: a·cous·ti·cal adj.a·cous·ti·cal·ly / -ik(ə)lē/ adv.