Ciao

The following analysis of the Italian word "ciao" is from here:

I often close letters with "ciao", which means both "hello; hi" and "bye; goodbye". When I do this, I am essentially saying "I am your slave". 

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 Italianschiavo, English Slav, slave and Old Venetian S-ciavón ("Slav"), from LatinSclavonia (“Slavonia”). Not related to Vietnamese chào (“hello, goodbye”).

Wiktionary 

The Italian salutation ciao, which is now popular in many parts of the world outside Italy, originated in the dialects of northern Italy. In the dialect of Venice, ciau literally means "servant, slave," and is also used as a casual greeting, "I am your servant." Dialectal ciau corresponds to standard Italian schiavo, "slave," and both words come from Medieval Latin sclāvus. Declaring yourself someone's slave might seem like an extravagant gesture today, but expressions such as Your obedient servant or Your servant, madam were once commonplace in English. Similarly, the Classical Latin word servus meaning "slave" is still used as an informal greeting in southern Germany and in Austria, the Czech Republic, Slovakia, Hungary, Poland, Romania, Ukraine, and other parts of central Europe that were formerly part of the Austro-Hungarian Empire. At the opposite end of the world, in Southeast and East Asia, one even finds words that originally meant "slave"or "your slave" but have developed into pronouns of the first person through their use in showing respect and humility. In Japanese, for example, the word boku is used to mean "I, me," especially by boys and young men, and it comes from a Middle Chinese word meaning "slave" or "servant" and now pronounced pú in Mandarin.

American Heritage Dictionary, 5th ed.