lesson
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Say the word coin out loud very slowly. Notice how your mouth starts wide and rounded, then quickly slides into an open smile?
That sliding motion happens because your voice is gliding between two different vowel positions in a single syllable.
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A diphthong is a special vowel team where two vowels work together to glide from one mouth shape to another.
The word comes from Greek diphthongos, meaning 'two sounds' or 'double voice'.
How do we spot these gliding sounds when reading giant multisyllabic words?
The /oy/ Sound: OI and OY
The /oy/ sound is usually spelled oi in the middle of a syllable, and oy at the end of a syllable.
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Because a diphthong makes one gliding vowel sound, you must never split the two letters when dividing syllables.
Let's decode the three-syllable word appointment step by step.
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What about the second big diphthong sound that shows up in words like flower and mountain?