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1. (Biochemistry) blood containing the Rh factor
2. (Biochemistry) a person having such blood
any of a group of antigens on the surface of red blood cells, those having inherited such antigens being designated Rh + (Rh positive) and those lacking them, a much smaller group, being designated Rh− (Rh negative) : transfused or fetal Rh + blood may induce a severe reaction in an Rh− individual.
[1940–45; so called because first found in the blood of rhesus monkeys]