Definition of Eigne
L. Fr. Eldest; eldest-bom. The term is of common occurrence in the old books. Thus, bastard eigne means an illegitimate son whose parents afterwards marry and have a second son for lawful issue, the latter being called mulier puisne (afterborn). Eigne is probably a corrupt form of the French “aine.” 2 Bl.Comm. 248.
That's the definition of Eigne in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.