Brother
Old English brōthor, of Germanic origin; related to Dutch broeder and German Bruder, from an Indo-European root shared by Latin frater .
wiktionary
From Middle English brother, from Old English brōþor, from Proto-West Germanic *brōþer, from Proto-Germanic *brōþēr (compare North Frisian Bröðer, West Frisian broer, Dutch broeder, German Bruder, Danish broder, Norwegian bror), from Proto-Indo-European *bʰréh₂tēr (compare Irish bráthair, Welsh brawd, Latin frāter, Ancient Greek φράτηρ(phrátēr), Armenian եղբայր(ełbayr), Tocharian A pracar, Tocharian B procer, Russian брат(brat), Lithuanian brolis, Persian برادر (barādar),Northern Kurdish bira, Sanskrit भ्रातृ(bhrātṛ)). Doublet of frater, friar, and pal.
etymonline
brother (n.)
Old English broþor, from Proto-Germanic *brothar (source also of Old Norse broðir, Danish broder, Old Frisian brother, Dutch broeder, Old High German bruodar, German Bruder, Gothic bróþar), from PIE root *bhrater-.
A stable word across the Indo-European languages (Sanskrit bhrátár-, Greek phratér, Latin frater, etc.). Hungarian barát is from Slavic; Turkish birader is from Persian.
In the few cases where other words provide the sense, it is where the cognate of brother had been applied widely to "member of a fraternity," or as an appellation of a monk (Italian fra, Portuguese frade, Old French frere), or where there was need to distinguish "son of the same mother" from "son of the same father." For example Greek adelphos, which probably originally was an adjective with phrater and meant, specifically, "brother of the womb" or "brother by blood," and became the main word as phrater became "one of the same tribe." Spanish hermano "brother" is from Latin germanus "full brother" (on both the father's and mother's side); Middle English also had brother-german in this sense.
Meaning "male person in relation to any other person of the same ancestry" in English is from late 14c. Sense of "member of a mendicant order" is from c. 1500. As a familiar term of address from one man to another, it is attested from 1912 in U.S. slang; the specific use among blacks is recorded from 1973.
