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|Sound change and alternation|
Crasis (//; from the Greek κρᾶσις, "mixing", "blending") is a type of contraction in which two vowels or diphthongs merge into one new vowel or diphthong, making one word out of two (univerbation). Crasis occurs in many languages, including Spanish, Portuguese, and French; it was first described in Ancient Greek.
In some cases, as in the French examples, crasis involves the grammaticalization of two individual lexical items into one. However, in other cases, like in the Greek examples, crasis is the orthographic representation of the encliticization and the vowel reduction of one grammatical form with another. The difference between them is that the Greek examples involve two grammatical words and a single phonological word, but the French examples involve a single phonological word and grammatical word.