You might be thinking of a diphthong, which is a combination of two vowel sounds within a single syllable.
Here's a breakdown:
* Diphthong: A sound formed by the gliding of the tongue from one vowel position to another. Examples include:
* "oi" in "boy"
* "ou" in "house"
* "ay" in "say"
Dighthong is not a recognized term in grammar or phonetics. If you encountered it, it's likely a misspelling of "diphthong."