Where does “brethren” come from?

brethren (Middle English) comes from Old English brōþor, from Proto-West Germanic brōþer, from Proto-Germanic brōþēr, from Proto-Indo-European bʰréh₂tēr — brother.

Ancestry of “brethren”, step by step

StepLanguageWordMeaning
1Old Englishbrōþorbrother
2Proto-West Germanicbrōþerbrother
3Proto-Germanicbrōþērbrother
4Proto-Indo-Europeanbʰréh₂tērbrother

Words derived from “brethren”

Every word from Proto-Indo-European bʰréh₂tēr →Every word from Proto-Germanic brōþēr →Every word from Proto-West Germanic brōþer →