Per Derksen, from Proto-Balto-Slavic *kuśnas, probably continuing an obscure Proto-Indo-European *kewḱ-. Cognate[1] with Latvian kusls (“stiff, small, weak”), Lithuanian kùšlas (“blind, weak, small”).
Trubachev proposes instead a connection to Proto-Slavic *kysělъ (“sour, bitter”) (or Proto-Slavic *kvasъ (“leaven”) in that matter) via semantic shift sour → overpassed its expiration date → late similar to Latin sērus (“late”) from Latin serum (“whey”).
Technically, could also reflect an earlier *kъtsьnъ akin to Proto-Slavic *kъsenь (“caviar, spawn”), Proto-Slavic *kutiti (“to push”), Proto-Slavic *kustriti (“to push, to incite”) and further Lithuanian kùtas (“fringe, hem”). Per Snoj, ultimately from Proto-Indo-European *kweh₂t- (“to seethe”), probably a t-extension of Proto-Indo-European *kewh₂- (“to hew”).
singular | masculine | feminine | neuter |
---|---|---|---|
nominative | *kъsьnъ | *kъsьna | *kъsьno |
genitive | *kъsьna | *kъsьny | *kъsьna |
dative | *kъsьnu | *kъsьně | *kъsьnu |
accusative | *kъsьnъ | *kъsьnǫ | *kъsьno |
instrumental | *kъsьnomь | *kъsьnojǫ | *kъsьnomь |
locative | *kъsьně | *kъsьně | *kъsьně |
vocative | *kъsьne | *kъsьno | *kъsьno |
dual | masculine | feminine | neuter |
nominative | *kъsьna | *kъsьně | *kъsьně |
genitive | *kъsьnu | *kъsьnu | *kъsьnu |
dative | *kъsьnoma | *kъsьnama | *kъsьnoma |
accusative | *kъsьna | *kъsьně | *kъsьně |
instrumental | *kъsьnoma | *kъsьnama | *kъsьnoma |
locative | *kъsьnu | *kъsьnu | *kъsьnu |
vocative | *kъsьna | *kъsьně | *kъsьně |
plural | masculine | feminine | neuter |
nominative | *kъsьni | *kъsьny | *kъsьna |
genitive | *kъsьnъ | *kъsьnъ | *kъsьnъ |
dative | *kъsьnomъ | *kъsьnamъ | *kъsьnomъ |
accusative | *kъsьny | *kъsьny | *kъsьna |
instrumental | *kъsьny | *kъsьnami | *kъsьny |
locative | *kъsьněxъ | *kъsьnaxъ | *kъsьněxъ |
vocative | *kъsьni | *kъsьny | *kъsьna |
singular | masculine | feminine | neuter |
---|---|---|---|
nominative | *kъsьnъjь | *kъsьnaja | *kъsьnoje |
genitive | *kъsьnajego | *kъsьnyję̇ | *kъsьnajego |
dative | *kъsьnujemu | *kъsьněji | *kъsьnujemu |
accusative | *kъsьnъjь | *kъsьnǫjǫ | *kъsьnoje |
instrumental | *kъsьnyjimь | *kъsьnǫjǫ | *kъsьnyjimь |
locative | *kъsьnějemь | *kъsьněji | *kъsьnějemь |
vocative | *kъsьnъjь | *kъsьnaja | *kъsьnoje |
dual | masculine | feminine | neuter |
nominative | *kъsьnaja | *kъsьněji | *kъsьněji |
genitive | *kъsьnuju | *kъsьnuju | *kъsьnuju |
dative | *kъsьnyjima | *kъsьnyjima | *kъsьnyjima |
accusative | *kъsьnaja | *kъsьněji | *kъsьněji |
instrumental | *kъsьnyjima | *kъsьnyjima | *kъsьnyjima |
locative | *kъsьnuju | *kъsьnuju | *kъsьnuju |
vocative | *kъsьnaja | *kъsьněji | *kъsьněji |
plural | masculine | feminine | neuter |
nominative | *kъsьniji | *kъsьnyję̇ | *kъsьnaja |
genitive | *kъsьnъjixъ | *kъsьnъjixъ | *kъsьnъjixъ |
dative | *kъsьnyjimъ | *kъsьnyjimъ | *kъsьnyjimъ |
accusative | *kъsьnyję̇ | *kъsьnyję̇ | *kъsьnaja |
instrumental | *kъsьnyjimi | *kъsьnyjimi | *kъsьnyjimi |
locative | *kъsьnyjixъ | *kъsьnyjixъ | *kъsьnyjixъ |
vocative | *kъsьniji | *kъsьnyję̇ | *kъsьnaja |