1. (n.) A male person who has the same father and mother with another person, or who has one of them only. In the latter case he is more definitely called a half brother, or brother of the half blood.

2. (n.) One related or closely united to another by some common tie or interest, as of rank, profession, membership in a society, toil, suffering, etc.; -- used among judges, clergymen, monks, physicians, lawyers, professors of religion, etc.

3. (n.) One who, or that which, resembles another in distinctive qualities or traits of character.

4. (v. t.) To make a brother of; to call or treat as a brother; to admit to a brotherhood.

Greek abbacomes abbot acquaintance adjunct advocate affiliate ally alter ego analogon analogue ascetic associate aunt auntie backer beadsman bedfellow belonger best friend blood brother bosom friend brethren brother-in-arms bub bubba bud buddy caloyer card-carrier card-carrying member cardholder casual acquaintance catechumen celibate cenobite charter member chum church member churchman churchwoman close acquaintance close copy close friend close match clubber clubman clubwoman coadjutor cognate cohort colleague committeeman communicant companion compatriot compeer complement comrade confederate confidant confidante confrere congenator congener consociate consort conventioneer conventioner conventionist conventual conventual prior coordinate correlate correlative correspondent counterpart country cousin cousin cousin once removed cousin twice removed crony daughter dues-paying member enlistee enrollee equivalent familiar father favorer fellow fellow creature fellow member fellowman first cousin foster brother frater fraternity man friar friend grand prior grandnephew grandniece granduncle great-aunt great-uncle guildsman half brother hermit hieromonach honorary member image initiate inseparable friend insider intimate joiner kid brother kin kindred spirit kinsman laic lay abbot lay brother lay sister layman laywoman life member like likeness lover mate member mendicant monastic monk mother near duplicate neighbor nephew niece nuncle nunks nunky obverse one of us other self pal palmer parallel parishioner partisan pendant pickup picture pilgrim pillar saint pillarist pledge prior reciprocal relation relative religieux religious repository second cousin second self secular sibling similitude simulacrum sis sissy sister sister-german sistern socius son sorority girl sorority woman soul mate stepbrother stepsister stylite such suchlike supporter sympathizer tally the like of the likes of twin unc uncle uncs uterine brother well-wisher