Reconstruction:Proto-Slavic/ovadъ

Morphologically from *o(b)- +‎ *(v)adъ. Proposed etymologies for the stem element:

• Miklošič, Brugmann, Zubatý: Inherited from Proto-Balto-Slavic *ṓˀdas (“biter, stinger”), either from Proto-Indo-European *h₃ed- (“to bite”) or possibly an o-grade of *h₁ed- (“to eat”). Cognate with Lithuanian úodas (“mosquito”), Latvian uôds, ods (“gnat, mosquito”). Compare also dialectal Belarusian вадзе́нь (vadzjénʹ, “gadfly”) (earlier *(v)adьňь).
• Pokorny: From Proto-Indo-European *wedʰ- (“to shove, to push”), akin to Sanskrit वध् (vadh, “to slay, to strike down”), Ancient Greek ὠθέω (ōthéō, “to push”).
• Machek: From a substrate language, possibly related to Latin tabānus (“gadfly”).

Trubachev alternatively interprets the word as a compound of *ov- (“sheep”) +‎ *adъ (“eater, biter”), since warble flies (and related insects) usually attack livestock.

*ovadъ m^[1]

1. biting insect (horsefly/stable fly/gadfly, hornet)

• *obadъ
• *ovodъ (East Slavic)

• *jadъ (“hate, anger”)
• *ědъ (“eating”), *ědьcь (“eater”)

• East Slavic:
  • Old East Slavic: оводъ (ovodŭ)
    • Belarusian: авадзе́нь (avadzjénʹ, “warble fly”), ава́д (avád); вадзе́нь (vadzjénʹ) (dialectal)
    • Russian: о́вад (óvad), о́вод (óvod)
    • Ukrainian: о́вад (óvad), о́від (óvid)
• South Slavic:
  • Old Church Slavonic: овадъ (ovadŭ), обадъ (obadŭ) (Serbian rendition)
  • Bulgarian: о́вад (óvad, “stable fly, hornet”) (dialectal)
  • Serbo-Croatian:

    Cyrillic script: о̏ба̄д

    Latin script: ȍbād

    • Kajkavian (Bednja): ebȃod
  • Slovene: obȃd (tonal orthography)
• West Slavic:
  • Old Czech: ovád (“horsefly”)
    • Czech: ovád (“horsefly”)
      • Bohemian (Chod dialect): hovád (“horsefly”)
  • Kashubian: òwôd
  • Polish: owad
  • Silesian: ôwada
  • Old Slovak: ovad
    • Slovak: ovad

• Vasmer, Max (1964–1973) “овод”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress
• Zhuravlyov, A. F., editor (2014), “*ovadъ”, in Этимологический словарь славянских языков [Etymological dictionary of Slavic languages] (in Russian), numbers 39 (*otъtęti – *ozgǫba), Moscow: Nauka, →ISBN, page 185
• Georgiev, Vladimir I., Duridanov, I. V., editors (1995), “овад”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volume 4 (мѝнго² – па̀дам), Sofia: Prof. Marin Drinov Pubg. House, →ISBN, page 743
• овад in Горох.ua (Етимологія)