Cachaça is a distilled spirit made from fermented sugarcane juice, similar to rum, and is Brazil's national drink. It's a word that immediately evokes a sense of Brazilian culture and festivity.
In the song, Gaia sings "Che mischio la cachaça con il bianco" (That I mix cachaça with white), which could refer to mixing the drink with a white mixer or perhaps even metaphorically mixing the vibrant Brazilian spirit with something more subdued. Its inclusion adds a unique, exotic flavor to the lyrics, hinting at the song's bossa nova influences and a longing for a passionate, perhaps bittersweet, experience.
"Bossa nostra" is a pun sitting right on top of the song. Bossa nova is the Brazilian sound Gaia grew up half inside; cosa nostra is the phrase for something kept quiet among the people it belongs to. Put together, they describe an affair nobody is allowed to see. The price gets stated flatly: "E la gente che passa non sa veramente / Quanto ci costa" (and the people walking past don't really know how much it costs us), and the cost is "Vederci per strada e fare finta di niente" (meeting in the street and pretending nothing is there).
Brazil is where the song goes to breathe. "Il cielo in una stanza in quell'hotel a Bahia" (the sky inside a room in that hotel in Bahia) borrows the title of Gino Paoli's old standard and drops it in a hotel eight thousand kilometres from Rome, and by the second verse she is "mischio la cachaça con il bianco" (mixing cachaça with white wine) while he is too tired to dance. Then the fantasy runs out. The bleakest line in the song is not exotic at all: "Siamo lontani nello stesso letto" (we are far apart in the same bed). What is left of the two of them is "Una goccia nell'Atlantico ormai" (just a drop in the Atlantic by now), and she asks him to explain love to her "come fosse una canzone in una lingua straniera" (as if it were a song in a foreign language), which is a very generous way of saying she no longer understands him.