What is defined as the smallest meaningful unit in a morphological system?

The smallest meaningful unit in a morphological system is referred to as a morpheme. Morphemes are the building blocks of words; they can be free or bound. A free morpheme can stand alone as a word (like "book" or "run"), while a bound morpheme cannot stand alone and must attach to another morpheme (like the prefix "un-" in "unhappy" or the suffix "-ed" in "walked"). Understanding morphemes is essential in morphology as it helps in analyzing how words are formed and how their meanings can change with the addition of different morphemes.

In contrast, a phoneme is a distinct unit of sound that can differentiate meaning but does not carry meaning itself, which is why it does not fit this definition. Phonology refers to the study of how sounds function in particular languages, but it does not involve meaning directly. Syntax deals with how words combine to form phrases and sentences rather than the smallest units of meaning. Therefore, morpheme is the appropriate choice when identifying the smallest meaningful unit in morphology.