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The word ciao comes from the Venetian language's s-ciàvo or s-ciào, Italian schiavo, slave. Originally it was used as a salutation (greetings, hello, good-bye) said by a servant to his boss, or mostly as a very formal greeting among the aristocracy when there was rank involved. Literally translated, the phrase sciao means, "I am your slave." From the times of its origin to now, it lost the s and became the more informal ciao, and became a very common greeting or good-bye among friends and relatives. The word s-ciào is still used in Venetian as an exclamation of resignation in unavoidable situations.

Ciao is now one of the main salutations of Serbo-Croatian and is commonly used in Brazil and Argentina, having arrived with the many Italian immigrants who came to the region. It is also used occasionally by English and French speakers and, only as a good-bye, quite frequently by younger Germans.