The syllable is a unit of pronunciation with one vowel sound. It forms part or the whole of a word. The syllable can be classified into three parts.
The three parts of the syllable are the onset, nucleus and coda. The nucleus and coda can be further classified into the rhyme. The onset and the coda are optional, but the nucleus is an essential part of the syllable.
The word pin has an onset, nucleus and coda. The onset is /p/, the nucleus is /I/ and the coda is /n/. In the word in there is no onset. The nucleus is /I/ and the coda is /n/. The word eye has no onset or coda. The nucleus is /aI/.
The syllable can be light or heavy. A light syllable consists of a short vowel. The heavy syllable consists of a long vowel, diphthong or syllable with a coda. If the syllable has a coda, it is closed and if it has no coda, it is open.
Syllable structure differs among languages. English allows the consonant cluster /sk/ in the onset and coda, but Spanish does not. The word school is thus escuela in Spanish.
The syllable is an important unit of phonology. Words with one syllable are monosyllabic. If they have two syllables, they are disyllabic and if they have three, they are trisyllabic. Long words with over three syllables are polysyllabic. The essential unit of the syllable is the nucleus.