The word derives from the Venetian phrase sciào vostro (in Italian schiavo vostro) or s-ciào su literally meaning "I am your slave". This greeting is analogous to the Latin Servus which is still used in a large section of Central/Eastern Europe. The expression was not a literal statement of fact, of course, but rather a perfunctory promise of good will among friends (along the lines "if you ever need my help, count on me"). The Venetian word for "slave", s-ciào (['st?ao]) or s-ciàvo, is cognate of the Italian schiavo and derives from Latin sclavus which originally indicated Slavic people, often used as slaves in the Mediterranean area and which replaced servus in Medieval Latin.
This greeting expression was eventually shortened to ciào, lost all its servile connotations and came to be used as an informal salutation by speakers of all classes. The word s-ciào is still used in Venetian and in the Lombard language as an exclamation of resignation, as in Oh, va be', s-ciào ("Oh, well, never mind!"). A Milanese proverb/tongue-twister says Se gh'inn gh'inn, se gh'inn no s-ciào ("If there is [money], there is; if there isn't, farewell! [there's nothing we can do]").