Where does “Братко” come from?

Братко (Bulgarian) comes from Bulgarian брат, from Proto-Slavic bratrъ, from Proto-Balto-Slavic brā́ˀtē, from Proto-Indo-European bʰréh₂tēr — brother.

Ancestry of “Братко”, step by step

StepLanguageWordMeaning
1Bulgarianбратbrother
2Proto-Slavicbratrъbrother
3Proto-Balto-Slavicbrā́ˀtēbrother
4Proto-Indo-Europeanbʰréh₂tērbrother
Every word from Proto-Indo-European bʰréh₂tēr →Every word from Proto-Balto-Slavic brā́ˀtē →Every word from Proto-Slavic bratrъ →