What is Bastard Eigne?

Legal Definition
Eng. law. Elder bastard. By the old English law, when, a man had a bastard son, and he afterwards married the mother, and by her had a legitimate son, the first was called a bastard eigne, or, as it is now spelled, aine, and the second son was called puisne, or since born, or sometimes he was called mulier puisne. See Mulier; Eigne, 2 Bl. Com. 248.
-- Bouviers Law Dictionary
Legal Definition
In old English law. Bastard elder. If a child was barn of an. illicit connection, and afterwanis the parente intermarried and had another son. the elder was called "bastard eigne," and the younger, "mulier puisne," i. e., afterwards bom of the wife. See 2 Bl. Comm. 248.
-- Black's Law Dictionary
Legal Definition
The eldest son born a bastard of parents who then marry and beget others.
-- Ballentine's Law Dictionary