Reconstruction:Proto-Slavic/kalъ

Unknown. No reliable non-Slavic cognates have been identified to date (including in Baltic languages, which is surprising considering some archaic features of the word).

Semantically close Ancient Greek πηλός (pēlós, “clay, mud, bog”) (also Doric πᾱλός (pālós), which could indicate possible derivation from *kʷālos) is unexplained as well, since derivation from a common IE **kʷeh₂los is prevented by accentuation (Hirt's law). Beekes suspected it to be a Pre-Greek (non-IE substrate) borrowing.

Something similar is Latin squālus (“dirty, unkempt”): there's no etymology, sematics seems to be close and according to de Vaan, sequence "squ-" indicates it isn't an inherited word. However, the root may be derived to squālor (“filth, roughness of the surface”) and squāma (“scale”) even though those lack an etymology as well.

Sanskrit काल (kāla, “black, very dark blue”) is either a Dravidian borrowing or a late development, thus unrelated.

*kȃlъ m^[1]

1. dirt

• *kaliti
• *kalina

• East Slavic:
  • Russian: кал (kal)
  • Ukrainian: кал (kal)
• South Slavic:
  • Old Church Slavonic:

    Cyrillic: калъ (kalŭ)

    Glagolitic: [Term?]

  • Bulgarian: кал (kal)
  • Macedonian: кал (kal)
  • Serbo-Croatian:

    Cyrillic script: ка̑л

    Latin script: kȃl

  • Slovene: kȃl
• West Slavic:
  • Czech: kal
  • Kashubian: kôł
  • Polish: kał
  • Slovak: kal

• Trubachyov, Oleg, editor (1983), “*kalъ”, in Этимологический словарь славянских языков [Etymological dictionary of Slavic languages] (in Russian), numbers 9 (*jьz – *klenьje), Moscow: Nauka, page 128
• Vasmer, Max (1964–1973) “кал”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress