Sant'allegria literally translates to "Saint Joy" or "Holy Joy." It's an interesting and somewhat unusual phrase because "allegria" (joy) is an abstract noun, not typically canonized as a saint.
In the context of the song, Ornella Vanoni personifies joy, elevating it to a sacred or revered status. By calling it "Sant'allegria," she imbues the feeling of joy with a spiritual significance, almost as if praying to it or acknowledging its divine presence amidst life's uncertainties and sorrows. This unique personification makes the word stand out and adds a poetic depth to the lyrics.
Vanoni spends this song asking for halves. She is waiting for someone to say something to her, and what she asks for keeps shrinking: "Un'altra frase, mezza frase, aspetterò" (Another sentence, half a sentence, I will wait), and then "Sperando che sia vera" (Hoping that it is true). That second line is the quiet catch. She has already lowered the price to almost nothing, and she still cannot be sure the little she gets will be honest.
Everything around her is moving, and most of it is coming down. Evening falls twice inside one line, "Scende, scende la sera ma è così breve stasera" (Evening falls, it falls, but tonight it is so short). A star drops out of the middle of a wish. The coast is "Nera, nera riviera, c'è chi spera e chi va" (Black, black shoreline, some people hope and some walk away), which sorts everyone into the two groups the song cares about. Even the title is a pair of small canonisations that refuse to stay put: "Sant'allegria, sant'amore che vai via" (Holy joy, holy love that goes away). Carlo Fava and Gianluca Martinelli wrote the Italian words over a melody by Arnaldo Antunes and Marisa Monte, and that Brazilian lightness is still in the arrangement, which is why a song this resigned never sounds heavy.