Arrepentida translates to "regretful" or "repentant." It's a key word in the song, even appearing in the title, and it captures the central theme of a past lover potentially regretting their actions.
The singer imagines a future where his ex-partner returns, full of regret, after having left him. This word is emotionally charged and directly relates to the song's narrative of heartbreak and potential vindication, making it very enticing for a learner.