Porphyrogenitism \Por`phy*ro*gen"i*tism\, 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]