Crasis

Crasis is a type of contraction in which two vowels or diphthongs merge into one new vowel or diphthong — making one word out of two. Crasis occurs in Portuguese and Arabic as well as in Ancient Greek, where it was first described.

In some cases, as in the French examples below, crasis involves the grammaticalization of two individual lexical items into one, but in other cases, as in the Greek examples, crasis is the orthographic representation of the encliticization and vowel reduction of one grammatical form with another. The difference between the two is that the Greek examples involve two grammatical words and a single phonological word and the French examples involve a single phonological word and grammatical word.