alliteration: [17] 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[alliteration etymology, alliteration origin, 英语词源]
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.