The one that cannot be further divided into smaller grammatically meaningful components is _________

The correct answer is a morpheme.

Step-by-Step Explanation:

1. Morpheme: A morpheme is defined in linguistics as the smallest grammatical unit in a language. It carries semantic meaning or serves a grammatical function and cannot be divided into smaller meaningful components. For example, in the word "unbreakable", "un-", "break", and "-able" are morphemes.

2. Phoneme: A phoneme is the smallest unit of sound that can distinguish one word from another (e.g., the sound /p/ in "pat"), but it does not possess inherent grammatical meaning on its own.

3. Diphthong: A diphthong refers to a sound formed by the combination of two vowels in a single syllable (e.g., the sound in "coin"), which is a phonetic concept rather than a grammatical or meaningful unit.

4. Syntax: Syntax refers to the set of rules, principles, and processes that govern the structure of sentences in a given language, which operates on a higher level than individual morphemes.

Therefore, the unit that cannot be further divided into smaller grammatically meaningful components is a morpheme.