Source : Webster's Revised Unabridged Dictionary (1913)

Alliteration \Al*lit`er*a"tion\, n. [L. ad + litera letter. See
   {Letter}.]
   The repetition of the same letter at the beginning of two or
   more words immediately succeeding each other, or at short
   intervals; as in the following lines: 

         Behemoth, biggest born of earth, upheaved His vastness.
                                                  --Milton.

         Fly o'er waste fens and windy fields.    --Tennyson.

   Note: The recurrence of the same letter in accented parts of
         words is also called alliteration. Anglo-Saxon poetry
         is characterized by alliterative meter of this sort.
         Later poets also employed it.

               In a somer seson whan soft was the sonne, I shope
               me in shroudes as I a shepe were.  --P. Plowman.

Source : WordNet®

alliteration
     n : use of the same consonant at the beginning of each stressed
         syllable in a line of verse; "around the rock the ragged
         rascal ran" [syn: {initial rhyme}, {beginning rhyme}, {head
         rhyme}]