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.
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.
a man who is a member of a religious order, but is not ordained. A Brother takes vows of poverty, chastity and obedience. He usually lives in community and is involved in some form of ministry or an apostolate.