porphyrogenitism, n. [LL. porphyro genitus, fr. Gr. ; purple + root of gi`gnesqai to be born.].
The principle of succession in royal families, especially among the Eastern Roman emperors, by which a younger son, if born after the accession of his father to the throne, was preferred to an elder son who was not so born. Sir T. Palgrave. [1913 Webster]