What is a contraction of two vowels (as the final and initial vowels of united words) into one long vowel, or into a dipthong; synæresis; as, cogo for coago called?

crasis — (Gram.) A contraction of two vowels (as the final and initial vowels of united words) into one long vowel, or into a dipthong; synæresis; as, cogo for coago. (Webster's 1913.)

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