Source : Webster's Revised Unabridged Dictionary (1913)

Eigne \Eigne\, a. [OF. aisn['e], ainsn['e], F. a[^i]n['e], fr.
   L. ante natus born before. Cf. {Esnecy}.]
   1. (Law) Eldest; firstborn. --Blackstone.

   2. Entailed; belonging to the eldest son. [Obs.]

   {Bastard eigne}, a bastard eldest son whose parents
      afterwards intermarry.