Reconstruction:Proto-Slavic/pьsъ

Unknown. There are several proposals:^[1]

• Connection of the stem *pьs- with the root of *pьstrъ (“variegated”), and thus ultimately from Proto-Indo-European *piḱ- (whence also Sanskrit पिशङ्ग (piśáṅga, “reddish, tawny”), पिश (piśá, “a sort of deer”)), the zero-grade of *peyḱ- (“to paint, mark”) (whence *pьsati (“to write”)). Thus the semantic shift occurred "spotted" > "dog" (perhaps compare Spot (“stereotypical English canine pet's name”)).
• Proto-Indo-European *pḱ-o-, the zero-grade of the root *speḱ- (“to see, watch”) (by Meillet).
• Proto-Indo-European *pḱ-u-, the zero-grade of *péḱu (“livestock”); compare Sanskrit पशु (páśu, “cattle”).

*pь̀sъ m^[1]

1. dog

   Synonym: *cucьkъ

• *pьsьcь (“puppy”)
• *pьsь (“doggy, canine”)
• *pьsovati

• East Slavic:
  • Old East Slavic: пьсъ (pĭsŭ), песъ (pesŭ)
    • Belarusian: пёс (pjos)
    • Russian: пёс (pjos)
    • Carpathian Rusyn: пес (pes)
    • Ukrainian: пес (pes)
• South Slavic:
  • Old Church Slavonic:

    Cyrillic: пьсъ (pĭsŭ)

    Glagolitic: ⱂⱐⱄⱏ (pĭsŭ)

  • Bulgarian: пес (pes)
  • Macedonian: пес (pes)
  • Serbo-Croatian:

    Cyrillic script: па̏с

    Latin script: pȁs

  • Slovene: pə̏s (tonal orthography)
• West Slavic:
  • Old Czech: pes
    • Czech: pes
  • Old Polish: pies
    • Polish: pies
    • Silesian: pies
  • Old Slovak: pes
    • Pannonian Rusyn: пес (pes)
    • Slovak: pes
  • Polabian: ṕås
  • Pomeranian:
    • Kashubian: pies
    • Slovincian: pjês
  • Sorbian:
    • Lower Sorbian: pjas
    • Upper Sorbian: pos

• Gluhak, Alemko (1993) “Proto-Slavic/pьsъ”, in Hrvatski etimološki rječnik [Croatian Etymology Dictionary] (in Serbo-Croatian), Zagreb: August Cesarec, →ISBN, page 468
• Vasmer, Max (1964–1973) “пес”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress