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.