Source : Webster's Revised Unabridged Dictionary (1913)

Again \A*gain"\ (?; 277), adv. [OE. agein, agayn, AS. ongegn,
   onge['a]n, against, again; on + ge['a]n, akin to Ger. gegewn
   against, Icel. gegn. Cf. {Gainsay}.]
   1. In return, back; as, bring us word again.

   2. Another time; once more; anew.

            If a man die, shall he live again?    --Job xiv. 14.

   3. Once repeated; -- of quantity; as, as large again, half as
      much again.

   4. In any other place. [Archaic] --Bacon.

   5. On the other hand. ``The one is my sovereign . . . the
      other again is my kinsman.'' --Shak.

   6. Moreover; besides; further.

            Again, it is of great consequence to avoid, etc.
                                                  --Hersche?.

   {Again and again}, more than once; often; repeatedly.

   {Now and again}, now and then; occasionally.

   {To and again}, to and fro. [Obs.] --De Foe.

   Note: Again was formerly used in many verbal combinations,
         as, again-witness, to witness against; again-ride, to
         ride against; again-come, to come against, to
         encounter; again-bring, to bring back, etc.

Source : WordNet®

again and again
     adv : repeatedly; "the unknown word turned up over and over again
           in the text" [syn: {over and over}, {over and over
           again}, {time and again}, {time and time again}]