Reconstruction:Proto-Slavic/sǫ-

From Proto-Balto-Slavic *sam-, from Proto-Indo-European *som (Derksen) or *sem- (“together, one”).

Baltic cognates include Lithuanian sam-, Latvian so-, Old Prussian sen-.

Indo-European cognates include Sanskrit सम् (sam, “together, at the same time”), Avestan 𐬵𐬀𐬨-‎ (ham-), 𐬵𐬀-‎ (ha-), Old Persian [Term?] (/⁠ham-⁠/), Ancient Greek ὁμοῦ (homoû, “together”), ἅμα (háma, “together with”), ἁ- (ha-), Latin semel (“once, a single time”).

*sǫ-

1. together

• *sъ(n), *sъ(n)- (“from, with”)

• East Slavic:
  • Belarusian: су- (su-)
  • Russian: су- (su-), со- (so-)
  • Ukrainian: су- (su-)
• South Slavic:
  • Old Church Slavonic:

    Old Cyrillic script: сѫ- (sǫ-), сън- (sŭn-) (decomposed nasalism, Ohrid Apostolarum) as in сънграждане (sŭngraždane, “fellow citizens”)

    Glagolitic script: ⱄⱘ- (sǫ-)

  • Bulgarian: съ- (sǎ-)
  • Serbo-Croatian:

    Cyrillic script: су-

    Latin script: su-

  • Slovene: so-
• West Slavic:
  • Old Czech: sú-
    • Czech: sou-
  • Kashubian: są-
  • Polish: są-
  • Slovak: sú-
  • Sorbian:
    • Upper Sorbian: su-
    • Lower Sorbian: su-

• Derksen, Rick (2008) Etymological Dictionary of the Slavic Inherited Lexicon (Leiden Indo-European Etymological Dictionary Series; 4), Leiden; Boston: Brill, →ISBN, →ISSN, page 462
• Vasmer, Max (1964–1973), “су-”, in Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), transl. & suppl. by Oleg Trubachyov, Moscow: Progress
• Chernykh, P. Ja. (1993), “су-”, in Историко-этимологический словарь русского языка [Historical-Etymological Dictionary of the Russian Language] (in Russian), volume 2 (панцирь – ящур), 3rd edition, Moscow: Russian Lang., →ISBN, page 215