Abraham refers to sarah his wife, as his sister, and clarifies it in Gen 20:2-12
Gen 20:2*And Abraham said of Sarah his wife, She is my sister: and Abimelech king of Gerar sent, and took Sarah.........11And Abraham said, Because I thought, Surely the fear of God is not in this place; and they will slay me for my wife's sake. 12And yet indeed she is my sister; she is the daughter of my father, but not the daughter of my mother; and she became my wife. 13And it came to pass, when God caused me to wander from my father's house, that I said unto her, This is thy kindness which thou shalt shew unto me; at every place whither we shall come, say of me, He is my brother.....15And Abimelech said, Behold, my land is before thee: dwell where it pleaseth thee. 16*And unto Sarah he said, Behold, I have given thy brother **a thousand pieces of silver: behold, he is to thee a covering of the eyes, unto all that are with thee, and with all other: thus she was reproved
Gen 11:26-31 appears to clarify that sarai was the daughter in law of Abram's father.
is this a clear OT example of Brother/sister being used for cousin.
if it is i think i am new to this one.
Gen 11:26And Terah lived seventy years, and begat Abram, Nahor, and Haran.
27Now these are the generations of Terah: Terah begat Abram, Nahor, and Haran; and Haran begat Lot. 28And Haran died before his father Terah in the land of his nativity, in Ur of the Chaldees. 29And Abram and Nahor took them wives: the name of Abram's wife was Sarai; and the name of Nahor's wife, Milcah, the daughter of Haran, the father of Milcah, and the father of Iscah. 30But Sarai was barren; she had no child.
31*And Terah took Abram his son, and Lot the son of Haran his son's son, **and Sarai his daughter in law*, his son Abram's wife; and they went forth with them from Ur of the Chaldees......
i found Augustines view on this and Jeromes
Augustine (Reply to Faustus - book XXII. 35)
35. It is waste of time to observe Faustus' remark, that Abraham falsely called Sara his sister; as if Faustus had discovered the family of Sara, though it is not mentioned in Scripture. In a matter which Abraham knew, and we do not, it is surely better to believe the patriarch when he says what he knows, than to believe Manichaeus when he finds fault with what he knows nothing about. Since, then, Abraham lived at that period in human history, when, though marriage had become unlawful between children of the same parents, or of the same father or mother, no law or authority interfered with the custom of marriage between the children of brothers, or any less degree of consanguinity, why should he not have had as wife his sister, that is, a woman descended from his father? For he himself told the king, when he restored Sara, that she was his sister by his father, and not by his mother. And on this occasion he could not have been led to tell a falsehood from fear, for the king knew that she was his wife, and was restoring her with honor, because he had been warned by God. We learn from Scripture that, among the ancients, it was customary to call cousins brothers and sisters. Thus Tobias says in his prayer to God, before having intercourse with his wife, 'And now, O Lord, Thou knowest that not in wantonness I take to wife my sister;"(1) though she was not sprung immediately from the same father or the same mother, but only belonged to the same family. And Lot is called the brother of Abraham, though Abraham was his uncle.(2) And, by the same use of the word, those called in the Gospel the Lord's brothers are certainly not children of the Virgin Mary, but all the blood relations of the Lord.(3)
Jerome (against Helvidius:17)
Just as Lot was called Abraham's brother, and Jacob Laban's, just as the daughters of Zelophehad received a lot among their brethren, just as Abraham himself had to wife Sarah his sister, for he says,(6) "She is indeed my sister, on the father's side, not on the mother's," that is to say, she was the daughter of his brother, not of his sister. Otherwise, what are we to say of Abraham, a just man, taking to wife the daughter of his own father ? Scripture, in relating the history of the men of early times, does not outrage our ears by speaking of the enormity in express terms, but prefers to leave it to be inferred by the reader: and God afterwards gives to the prohibition the sanction of the law, and threatens,(1) "He who takes his sister, born of his father, or of his mother, and beholds her nakedness, hath commited abomination, he shall be utterly destroyed. He hath uncovered his sister's nakedness, he shall bear his sin."