Reconstruction:Proto-Slavic/sǫpъ

Probably deverbal from a nasalized variant of onomatopoeia *so(p)ti, *sopěti (“to wheeze”), given that, as the vowel of the bird-name changed to и (i) in East Slavic, so the verb is replaced with the variant сипѣ́ть (sipě́tʹ), сипі́ти (sipíti, “to hiss”).

*sǫpъ m

1. vulture

• *sǫpiti (“to scowl”)

• East Slavic:
  • Old East Slavic:
    • Belarusian: сіп (sip)
    • Russian: сип (sip), суп (sup)
    • Ukrainian: сип (syp), суп (sup)
• South Slavic:
  • Old Church Slavonic:

    Old Cyrillic script: сѫпъ (sǫpŭ)

    Glagolitic script: ⱄⱘⱂⱏ (sǫpŭ)

  • Serbo-Croatian:

    Cyrillic script: су̏п

    Latin script: sȕp

• West Slavic:
  • Old Czech: sup
    • Czech: sup
  • Kashubian: sãp
  • Polabian:
  • Polish: sęp
  • Slovak: sup
  • Sorbian:
    • Lower Sorbian: sup
    • Upper Sorbian: sup

• Melnychuk, O. S., editor (2006), “суп”, in Етимологічний словник української мови [Etymological Dictionary of the Ukrainian Language] (in Ukrainian), volume 5 (Р – Т), Kyiv: Naukova Dumka, →ISBN, page 476
• Melnychuk, O. S., editor (2006), “сип”, in Етимологічний словник української мови [Etymological Dictionary of the Ukrainian Language] (in Ukrainian), volume 5 (Р – Т), Kyiv: Naukova Dumka, →ISBN, page 239
• Vasmer, Max (1964–1973) “сип”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress
• Todorov, T. A., Racheva, M., editors (2010), “супя се”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volume 7 (слòво – теря̀свам), Sofia: Prof. Marin Drinov Pubg. House, →ISBN, page 579