Webster's Revised Unabridged Dictionary · 1913

Alliteration

Alliteration ({not transcribed}) , noun

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

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.