0 someone who is related to you by birth rather than through marriage or another relationship such as adoption (= becoming the legal parent of a child who is not your own):
The study looked at genetic data from families that have suffered three, four, even as many as eight cases of lung cancer among blood relatives.
Whether the kidney donor is a blood relative, a relative by marriage or a friend there can be issues.
William Duke of Normandy insisted that Edward the Confessor, who was a distant blood relative, had also promised the succession to him.
It transpired that a relative - not a blood relative, but a relative by marriage - was a historian and had kept all the letters from Russia to my grandfather.
