Commenting on the use of αδελφος/αδελφη (brother/sister) in the Pauline corpus, Reidar Aasgaard noted that:
Of these 122 instances of the αδελφ-root, natural siblings account for
only two, in both instances brothers of Christ, 1 Cor. 9.5; Gal. 1.19. The
rest, 120 instances, are used in a metaphorical sense, usually in the form of
αδελφη, αδελφος, and αδελφοι. (Reidar Aasgaard, “My Beloved Brothers and
Sisters!”: Christian Siblings in Paul [Early Christianity in Context;
Journal for the Study of the New Testament Supplement Series 265; London:
T&T Clark, 2004], 3)
