diluvierà literally means "it will pour" or "it will flood". It's the future tense of the verb diluviare, which comes from the noun diluvio (a deluge or flood).
In the song, frontman Damiano sings the beautifully contradictory line, "Sotto il sole poi diluvierà" (Under the sun then it will pour). This powerful imagery suggests a sudden, overwhelming wave of sadness that washes over everything, even in a moment that should be bright. It's a poetic way to describe emotional turmoil and a truly unforgettable word from the track.
This song is a massive, emotional power ballad about distance and things left unsaid. The singer feels someone pulling away, and it's driving him crazy. He accuses them of a specific mistake: "l'errore tuo / È stato amarmi come se domani / il mondo fosse uguale / a com'era ieri" (your mistake / was to love me as if tomorrow / the world would be the same / as it was yesterday). It's a really interesting way of saying their partner couldn't handle change, and that's what broke them.
The whole song is filled with this feeling of desperation. He begs to be allowed to just get lost in his feelings, to "perdere / dentro l'acqua del mare" (get lost / inside the sea water). He feels this huge need to scream "le parole lontane" (the distant words) at this person, but he can't, because they are just too far away. He even calls out for a character named Marlena to take him home because he's scared and cold, showing a moment of pure vulnerability amidst all the rock and roll angst.