Source : Webster's Revised Unabridged Dictionary (1913)

Survival \Sur*viv"al\, n. [From {Survive}.]
   1. A living or continuing longer than, or beyond the
      existence of, another person, thing, or event; an
      outliving.

   2. (Arh[ae]ol. & Ethnol.) Any habit, usage, or belief,
      remaining from ancient times, the origin of which is often
      unknown, or imperfectly known.

            The close bearing of the doctrine of survival on the
            study of manners and customs.         --Tylor.

   {Survival of the fittest}. (Biol.) See {Natural selection},
      under {Natural}.

Source : WordNet®

survival of the fittest
     n : a natural process resulting in the evolution of organisms
         best adapted to the environment [syn: {survival}, {natural
         selection}, {selection}]