Who knew that Italian ciao was a variation of schiavo "(I am your) servant" from medieval Latin sclavus "slave".
slave was borrowed from Old French esclave, which is related to the Latin sclavus. The Latin word was borrowed into English as Slav.
Further etymology of sclavus is uncertain. In my previous post I write that Slav and slave seem to be derived from Proto-Slavic *slovo "word" or *slava "fame, glory" but I think I was wrong. The OED says Old Slavic Slovēne is supposed to be derived from slovo, but is it really? The whole thing is a bit of a muddle.