Reconstruction:Proto-Slavic/lopъ

Per Vasmer, of onomatopoeic origin.

The secondary meaning “gulping, devouring” is comparable with Latvian lepêt (“to eat vigorously”), Lithuanian lapénti (“to absorb”), Proto-Germanic *lapōną (“to lap, to slurp”), themselves onomatopoeic. Likely further akin to Ancient Greek λᾰ́πτω (lắptō, “to gulp, drink greedily”)

*lopъ m

1. smack, slap, spank

   Synonym: *xlopъ

2. (sound of) gulping, swallowing

• *lopati (“to rattle; to gulp, to swallow”), *lopiti (“to clap, to bang, to strike”)
  • *lopъka (“clot, wad”)
  • *lopę/*lopьnь (“loafer, slacker”)
• *lopьjь (“torrent, downpour”)
• *lopotь, *lopotьje, *lopota (“rag, tatter, frazzle cloth”)

• East Slavic:
  • Belarusian: лоп (lop)
  • Russian: лоп (lop) (colloquial)
  • Ukrainian: лоп (lop)
• South Slavic:
  • Bulgarian: лоп-лоп (lop-lop)
    • ⇒ Bulgarian: лоп (lop, “robbery, plunder”) (dialectal)
  • Serbo-Croatian:

    Cyrillic script: ло̏п

    Latin script: lȍp

  • Slovene: lòp

• Vasmer, Max (1964–1973), “лопать”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress
• Trubachyov, Oleg, editor (1990), “*lopъ I”, in Этимологический словарь славянских языков [Etymological dictionary of Slavic languages] (in Russian), numbers 16 (*lokadlo – *lъživьcь), Moscow: Nauka, →ISBN, page 77
• Georgiev, Vladimir I., editor (1986), “лоп-лоп”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volume 3 (крес¹ – мѝнго¹), Sofia: Bulgarian Academy of Sciences Pubg. House, page 470
• Snoj, Marko (2016), “lópiti”, in Slovenski etimološki slovar [Slovenian Etymology Dictionary] (in Slovene), 3rd edition, https://fran.si

From Proto-Balto-Slavic *lápas (“leaf”),^[1] cognate with Lithuanian lãpas (“leaf”), Latvian lapa (“leaf, sheet of paper”). Probably akin to Proto-Germanic *lappô (“lap, rag”), Proto-Germanic *lattō (“lath, shutter, board”). C. D. Buck suggests further relationship to Ancient Greek λέπω (lépō, “to peel”), ultimately from Proto-Indo-European.

*lopъ m^[2]

1. (regional) plant, herb with large bulbous leaves

• *lopuxъ, *lopunъ (“burdock”)
• *lopurъ (“water lilly”)
• *lopěnъ (“mullein”)
• *lopata (“shovel”)
• *lopъta (“ball, orb”), *loputa (“valve”)

• *lapa (“paw”)

• South Slavic:
  • Bulgarian: лоп (lop, “butterbur”) (dialectal)
  • Macedonian: лоп (lop, “water rose”)

• Trubachyov, Oleg, editor (1990), “*lopъ II”, in Этимологический словарь славянских языков [Etymological dictionary of Slavic languages] (in Russian), numbers 16 (*lokadlo – *lъživьcь), Moscow: Nauka, →ISBN, page 77
• Georgiev, Vladimir I., editor (1986), “лоп¹”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volume 3 (крес¹ – мѝнго¹), Sofia: Bulgarian Academy of Sciences Pubg. House, page 470
• “lapas”, in Lietuvių kalbos etimologinio žodyno duomenų bazė [Lithuanian etymological dictionary database], 2007–2012