What is the smallest unit of sound that affects meaning called?

The smallest unit of sound that affects meaning is referred to as a phoneme. Phonemes are the distinct sounds in a language that can differentiate one word from another. For instance, changing the initial sound in the word "pat" from /p/ to /b/ results in a different word, "bat." This capability to change meaning through sound is what defines a phoneme.

In contrast, a morpheme is the smallest unit of meaning in a language, such as a root word or a prefix. A syllable refers to a unit of pronunciation that typically contains a vowel sound and may or may not include surrounding consonants. A lexeme is the base form of a word without any inflections, encompassing its dictionary meaning. Understanding these distinctions helps clarify why phonemes are crucial in determining how sounds contribute to meaning in language.