From Greek 'akouein' (to hear), tracing to PIE *hkous- — an ancient root linking hearing to sharpness.
Relating to sound or the sense of hearing; of a musical instrument, producing sound without electrical amplification.
From French 'acoustique,' from Greek 'akoustikos' (pertaining to hearing), from 'akouein' (to hear), from 'akousis' (hearing). The Greek verb 'akouein' traces to a Proto-Indo-European root *h₂ḱous- meaning 'to hear,' which also produced Latin 'acūmen' (sharpness, keenness) through a related sense of perceptual sharpness. The word entered English in the early seventeenth century as a technical term in natural philosophy before broadening to general
The Greek root 'akouein' (to hear) is also the source of the rare English medical term 'acousia,' meaning the faculty of hearing, and of 'acousma,' a hallucinated sound. The same root may be distantly related to the 'acu-' in 'acute,' both sharing a PIE sense of sharpness of perception.