Ciao is a word I grew up hearing in both English- and French-speaking Canada (although always to say goodbye, never hello—whereas the Italians use it for both). I was a little surprised to also hear it very commonly used as a way to say goodbye in Colombia when I went there earlier this year (only they spell it chao).
The word has apparently been adopted in dozens of languages. As described in this article from language-learning app Babbel, its origin is a bit dark: it comes from the Venetian s’ciao vostro—I am your slave. The meaning was apparently more sociable than it sounds.
Ernest Hemingway is often credited with introducing it into English in 1929 with his novel A Farewell to Arms (though it seems he consistently misspelled it “ciaou”). The Italian diaspora and postwar tourism to Italy are also credited with seeding the word all over the globe.
But surely there are many such words that have spread around the world with their diasporas. Few have had the lasting success of ciao. I can’t help but feel the nature of the word itself must contribute—it is short, melodic, and easy to say.
Ciao.