Where does “тверезъ” come from?

тверезъ (Old East Slavic) comes from Old East Slavic терезвъ, from Proto-Slavic terzvъ, from Proto-Slavic -vъ, from Proto-Balto-Slavic *-was, from Proto-Indo-European -wós — Creates adjectives from verb stems.

Ancestry of “тверезъ”, step by step

StepLanguageWordMeaning
1Old East Slavicтерезвъ—
2Proto-Slavicterzvъsober
3Proto-Slavic-vъFrom thematic declension of u-stem...
4Proto-Balto-Slavic*-was—
5Proto-Indo-European-wósCreates adjectives from verb stems
Every word from Proto-Indo-European -wós →Every word from Proto-Slavic -vъ →Every word from Proto-Slavic terzvъ →