0-grade of Proto-Indo-European *bʰeh₂ǵos, which in the case of Slavic meant elderberry bush. Cognates include Gaulish bagos, Ancient Greek φηγός (phēgós), Latin fāgus, Proto-Germanic *bōkō (> German Buche, Norwegian bøk) which mean beech or oak. From the same root, but with a drifted meaning, is English book. Several Slavic languages have also borrowed from Germanic *bukъ (“beech”) (e.g. Russian бук (buk), Bulgarian бук (buk), Polish buk), which is ultimately of the same origin.
- South Slavic: