Ciao

google

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Italian, dialect alteration of schiavo ‘(I am your) slave’, from medieval Latin sclavus ‘slave’.

wiktionary

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Borrowed from Italian ciao(“hello, goodbye”), from Venetian ciao(“hello, goodbye, your (humble) servant”), from Venetian s-ciao / s-ciavo(“servant, slave”), from Medieval Latin sclavus(“Slav, slave”), related also to Italian schiavo, English Slav, slave and Old Venetian S-ciavón ("Slav"), from Latin Sclavonia(“Slavonia”). Not related to Vietnamese chào(“hello, goodbye”).

etymonline

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ciao (interj.)

parting salutation, 1929, dialectal variant of Italian schiavo "(your obedient) servant," literally "slave," from Medieval Latin sclavus "slave" (see slave (n.)).