Source : Webster's Revised Unabridged Dictionary (1913)

Firstborn \First"born`\, a.
   First brought forth; first in the order of nativity; eldest;
   hence, most excellent; most distinguished or exalted.

Source : WordNet®

firstborn
     adj : first in order of birth; "the firstborn child" [syn: {eldest}]
     n : the offspring who came first in the order of birth [syn: {eldest}]