(dated, chiefly historical) A person considered three-fourths white, having one non-white grandparent.
1938, Xavier Herbert, Capricornia, Chapter V, p. 63; Chapter VIII, p. 120 https://archive.org/details/capricornianovel00herb
Diana was a black quadroon, her father being a blackfellow.
He was the father of four quadroons who were regarded as half-castes because the lighter part of their mother's blood was Asiatic, and he was only too well aware of what their future would be should he desert them.
adjective
(dated, chiefly historical) Of or related to quadroons.