BROTHER, a male person in his relation to the other children of the same father and mother. "Brother" represents in English the Teutonic branch of a word common to the Indo-European languages, of. Ger. Bruder, Dutch broeder, Dan. and Swed. broder, etc. In Celtic languages, Gaelic and Irish have brathair, and Welsh brawd; in Greek the word is "phratêr", in Lat. frater, from which come the Romanic forms, Fr. frère, Ital. fratello; the Span. fray, Port. frei, like the Ital. frate, fra, are only used of "friars." The Span. hermano and the Port. irmao, the regular words for brother, are from Lat. germanus, born of the same father and mother. The Sanskrit word is bhratar, and the ultimate Indo-European root is generally taken to be bhar, to bear (cf. M. H. Ger. barn, Scot, bairn, child, and such words as "birth," "burden"). "Brother" has often been loosely used of kinsmen generally, or for members of the same tribe; also for quite fictitious relationships, e.g. "blood-brothers," through a sacramental rite of mutual blood-tasting, "foster-brothers," because suckled by the same nurse. Christianity, through the idea of the universal fatherhood of God, conceives all men as brothers; but in a narrower sense "the brethren" are the members of the Church, or, in a narrower still, of a confraternity or "brotherhood" within the Church. This latter idea is reproduced in those fraternal societies, e.g. the Freemasons, the members of which become "brothers" by initiation. "Brother" is also used symbolically, as implying equality, by sovereigns in addressing one another, and also by bishops.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)