Endrino refers to the sloe, a dark, tart fruit, or the blackthorn bush it grows on. It's a less common word, especially in song lyrics, making it quite unique and memorable.
In the song, it's used to describe the color of hair: "Y aquellas trenzas de pelo endrino" (And those braids of sloe-colored hair). This evokes a deep, dark, almost black hue, adding a poetic and slightly melancholic touch to the description of the lost love's hair.
Buika's "La Falsa Moneda" is a powerful song about a love that has gone very, very wrong. The singer compares their former lover to a "falsa moneda" [false coin] – something that "de mano en mano va y ninguno se la queda" [goes from hand to hand and no one keeps it]. It's a blunt and cutting image, showing how worthless and untrustworthy this person is.
The lyrics tell a story of deep betrayal and the struggle to move on. The singer describes having "cruza'os los brazos para no matarla" [crossed their arms not to kill her] and "cerraos los ojos para no llorar" [closed their eyes not to cry], showing intense pain and a fight for control. They even recall kissing the "negros zarcillos finos" [fine black earrings] and "aquellas trenzas de pelo endrino" [those blackthorn hair braids] that the lover left behind. The song ends with the singer inflicting pain on themselves, "se clavó las uñas, en el corazón" [they dug their nails into their heart], just to avoid calling out to the person who hurt them. It's a raw look at the agony of a love that turned into a curse.