A morpheme is the smallest meaningful unit in a language. Morphemes can be thought of as the building blocks of meaning and can be a standalone word or an affix – a prefix or suffix – that carries lexical or grammatical meaning. For example, the word cat is a morpheme in English because it has lexical meaning on its own and cannot be broken down into smaller pieces. The word cats has two morphemes, the lexical morpheme cat and the suffix s, which is a grammatical morpheme meaning plural.