alliteration:  Alliteration is an anglicization of alliterātiō, a modern Latin coinage based on the prefix ad- ‘to’ and litera ‘letter’ – from the notion of an accumulation of words beginning with the same letter. The verb alliterate is an early 19th-century back-formation from alliteration. => letter
1650s, "a begining with the same letter," from Modern Latin alliterationem (nominative alliteratio), noun of action from past participle stem of alliterare "to begin with the same letter," from Latin ad- "to" (see ad-) + littera (also litera) "letter, script" (see letter). Formed on model of obliteration, etc. Related: Alliterational.