What is the smallest distinctive sound unit in a language?

The smallest distinctive sound unit in a language is the phoneme. Phonemes are the basic building blocks of speech that differentiate meaning between words. For example, in English, the words "bat" and "pat" differ by a single phoneme – the initial sounds /b/ and /p/. This distinction is crucial because it illustrates how phonemes can change the meaning of words in language.

In contrast, other terms such as morphemes refer to the smallest units of meaning, which can be entire words or prefixes and suffixes. Syllables are larger units of sound that typically contain a vowel sound and may consist of one or more phonemes. Lexemes represent the abstract idea of a word or phrase in a language's vocabulary, but they are not specifically tied to sound units. Therefore, phoneme is the most accurate choice as it specifically refers to the smallest segment of sound that can convey meaning changes in spoken language.