loud: [OE] The underlying meaning of loud is ‘heard, audible’ – for it goes back ultimately to an Indo-European *klu- ‘hear’ (source also of English listen). The past participial form based on this, *klūtós, passed into prehistoric West Germanic as *khluthaz, which has since differentiated into German laut, Dutch luid, and English loud. => listen[loud etymology, loud origin, 英语词源]