Definition and background:
A characteristic of ancient Northern European poetry such as Beowulf consisting of the use of words with the same initial letter. This principle was adopted by Richard Wagner in Der Ring des Nibelungen, for example, "Nach W elten- Wonne mein W unsch verlangte aus w ild w ebendem Bangen."
For more information on the music term "Alliteration" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary