What term refers to the occurrence of the same letter or sound at the beginning of adjacent or closely connected words?

The term that refers to the occurrence of the same letter or sound at the beginning of adjacent or closely connected words is alliteration. This literary device is commonly used in poetry, prose, and songs to create rhythm, enhance mood, and emphasize particular phrases or themes. For instance, phrases like "Peter Piper picked a peck of pickled peppers" showcase alliteration through the repetition of the 'p' sound, making the phrase memorable and engaging.

While synonyms refer to words that have similar meanings, acronyms are formed from the initial letters of a series of words, and vocabulary pertains to the set of words known or used by a person or group. These concepts do not relate to the phonetic repetition characteristic of alliteration.