Siglo literally means "century". It's a great example of a hyperbole, a figure of speech that uses extreme exaggeration to make a point.
In this passionate ballad, Chayanne sings "Un día es un siglo sin ti" (A day is a century without you). He uses this dramatic comparison to express the unbearable and seemingly endless pain of being separated from the one he loves. This powerful metaphor is what makes the song so memorable.
Puerto Rican pop star Chayanne goes all out in this track with an unapologetic plea for forgiveness. He admits right from the start that he has concocted excuse after excuse just to stay in the picture: Mil y un historias me he inventado para estar aquí ("I've made up a thousand and one stories to be here"). He knows he messed up, acknowledging Sé que piensas que no he sido sincero ("I know you think I haven't been honest"), but now that his partner is gone, the regret is eating him alive. There is no subtle pride here; he simply throws his pride out the window and leaves the door wide open for their return.
The real centerpiece of the track is how wildly out of proportion time feels when you miss someone you love. Chayanne leans into total hyperbole with the chorus line Un día es un siglo sin ti ("One day is a century without you"). That is definitely dramatic, but anyone who has ever stared at an empty room after a breakup knows that twenty-four hours can feel endless. He begs for a fresh start with Ya lo que pasó, pasó, rescatemos lo que nos unió ("What happened, happened; let's rescue what brought us together"), arguing that the heartbreak actually helped him mature into someone new: Me has hecho crecer, es que no soy el mismo de ayer ("You made me grow; I'm not the same person I was yesterday").