Reconstruction:Proto-Slavic/verdьnъ

South Slavic isogloss, with dubious origin. The main two hypotheses for its etymology are:

• Native origin: According to St. Mladenov, from Proto-Indo-European *werdʰ- (“to raise”), cognate with Sanskrit वर्धति (vardhati, “to grow, to elevate”), Avestan 𐬬𐬀𐬭𐬆𐬛𐬀𐬌𐬙𐬌 (varədaⁱti, “to enlarge”). Probably akin to Proto-Slavic *verdъ, though, certainly not in its attested meaning wart, wound. See there for further discussion.
• Borrowing: Built on the basis of Old High German werd (“worth”), from Proto-Germanic *werþaz. Probably borrowed around 9th century.

Georgiev and Skok remain inconclusive.

*verdьnъ

1. worthy

• *verdьnostь, *verdьnota (“worth”)

• *verděti (“to be worth”)
• *verdati (“to estimate”)

• South Slavic:
  • Bulgarian: вре́ден (vréden) (dialectal)
  • Macedonian: вреден (vreden)
  • Serbo-Croatian:

    Cyrillic script: врије́дан

    Latin script: vrijédan

  • Slovene: vrẹ́den

• Georgiev, Vladimir I., editor (1971), “вреден²”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volume 1 (А – З), Sofia: Bulgarian Academy of Sciences Pubg. House, →ISBN, page 184
• Skok, Petar (1973), “vrijedan”, in Etimologijski rječnik hrvatskoga ili srpskoga jezika [Etymological Dictionary of the Croatian or Serbian Language] (in Serbo-Croatian), volumes 3 (poni² – Ž), Zagreb: JAZU, page 625
• Snoj, Marko (2016), “vrẹ́den”, in Slovenski etimološki slovar [Slovenian Etymology Dictionary] (in Slovene), 3rd edition, https://fran.si

From *verdъ (“harm”) +‎ *-ьnъ.

*verdьnъ

1. harmful
2. malicious

• *verdina (“damage”)
• *verdьnostь (“harm, malice”)

• *verditi (“to cause harm, to injure”)
• *verditeľь (“pest”)
• *verdovъ (“ulcerous”)

• South Slavic:
  • Old Church Slavonic:

    Old Cyrillic script: врѣдьнъ (vrědĭnŭ)

    • → Russian: вре́дный (vrédnyj)
      • → Polish: wredny
  • Bulgarian: вре́ден (vréden)
• West Slavic:
  • Polish: wrzedny (Middle Polish), wrzodny (rare)

• Georgiev, Vladimir I., editor (1971), “вреден¹”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volume 1 (А – З), Sofia: Bulgarian Academy of Sciences Pubg. House, →ISBN, page 184
• Vasmer, Max (1964–1973), “вред”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress
• Snoj, Marko (2016), “vredník”, in Slovenski etimološki slovar [Slovenian Etymology Dictionary] (in Slovene), 3rd edition, https://fran.si