From Proto-Baltic *klus-, from Proto-Indo-European *ḱlew- (“to sound, to hear”) (whence klausīt (“to obey”), q.v., klausīties (“to listen”), klust (“to be silent”), more frequently apklust), with an extra -s. The semantic evolution of klust, and consequently also of kluss, was probably: “to hear” > “to listen” > “to be quiet (in order to listen).” Cognates include Lithuanian klùsas (“hard of hearing, deaf”), klusùs (“hearing”), klùsti (“to obey, to be obedient”), Old Prussian poklusman (“hearing, obedient”) (neut. pl. nom.).