Final Answer:
A syll-able that has two vowel sounds slurred together and treated as a single vowel is called a di-phth-ong.
Step-by-step explanation:
A di-phth-ong is a complex vowel sound that begins with one vowel sound and glides into another within the same syllable. It involves a smooth transition between two vowel sounds, and both sounds are perceived as a single, gliding sound.
Examples of di-phth-ongs include the "oi" in "coin" or the "ou" in "cloud." Di-phth-ongs add variety and nuance to pronunciation, and their recognition is essential in understanding phonetics and phonology. This lin-guis-tic concept is fundamental to the study of vowels and syll-abic structure in languages.