In language, alliteration refers to repetition of a particular sound in the first syllables of a series of words and/or phrases. Alliteration has historically developed largely through poetry, in which it more narrowly refers to the repetition of a consonant in any syllables that, according to the poem's meter, are stressed, as in James Thomson's verse "Comedragging the lazy languid Line along".
Alliteration is usually distinguished as and within from the mere repetition of the same sound in positions other than the beginning of each word whether a consonant, as in "some mammals are clammy" (consonance) or a vowel, as in "yellow wedding bells" (assonance); but the term is sometimes used in these broader senses. Alliteration may also include the use of different consonants with similar properties (labials, dentals, etc.) or even the unwritten glottal stop that precedes virtually every word-initial vowel in the English language, as in the phrase "Apt alliteration's artful aid" (despite the unique pronunciation of the "a" in each word).
Alliteration is commonly used in many languages, especially in poetry. Alliterative verse was an important ingredient of poetry in Old English and other old Germanic languages like Old High German, Old Norse, and Old Saxon. On the other hand, its accidental occurrence is often viewed as a defect.