broth·er 
(brŭthər)
(brŭthər)n. pl. broth·ers
1. A male having the same parents as another or one parent in common with another.
2. pl. also breth·ren (brĕthrən) One who shares a common ancestry, allegiance, character, or purpose with another or others, especially:
a. A kinsman.
b. A fellow man.
c. A fellow member, as of a fraternity, trade union, or panel of judges on a court.
d. A close male friend; a comrade.
e. A fellow African-American man or boy.
3. pl. also brethren Something, such as a corporation or institution, that is regarded as a member of a class: "A station that ... relies on corporate contributions or advertising to survive runs the risk of becoming virtually indistinguishable from its commercial brethren" (W. John Moore).
4.
a. Abbr. Br. or Bro. A lay member of a religious order of men.
b. pl. also brethren A fellow member of the Christian church.
[Middle English, from Old English brōthor; see bhrāter- in the Appendix of Indo-European roots.]