dark

• Russian
  тёмныйtëmnyj

  ˈtʲomnɨjinherited
• Ukrainian
  те́мнийtemnyj

  ˈtɛmnɪjinherited
• Polish
  ciemny

  ˈtɕɛmnɨinherited
• Czech
  tmavý

  ˈtmaviːinherited

  Built on tma 'darkness' with another suffix; temný is literary.

• Bosnian-Croatian-Serbian
  tamanтаман

  ˈtamaninherited
• English
  dark

Sound laws at work

• The fall of the yers
• e → o before a hard consonant (ё)