köken: selkä (“back”) + sauna (“sauna”), from phrases like "saada selkään" which means to get spanked, but literally to "get it into the back"; sauna is probably used to symbolize heat. Compare the similarly formed Livvi perzekyly.
köken: Etymology tree Proto-Indo-European *bʰeyh₂- Proto-Balto-Slavic *bī́ˀtei Proto-Slavic *bìti Old Church Slavonic бити (biti) Bulgarian би́я (bíja)deverb. Proto-Indo-European *bʰeyh₂- Proto-Indo-European *bʰoyh₂ós Proto-Balto-Slavic *bajas Proto-Slavic *bòjь Bulgarian бой O-grade deverbal of би́я (bíja, “to beat”). Diachronically, inherited from Proto-Slavic *bojь.