malsín

tattler, stool pigeon, informer

“Justo fue que el malsín pagase con su vida el precio de sus denuncias, que nos pusieron en tanto peligro.” — It was just that the informer paid with his life for his denunciations, which put us in such danger.

Related: malsinar, malsindad, malsinería

Inherited from Old Spanish, a slang term spread in the 14th century from the Jewish quarters, borrowed from Hebrew מַלְשִׂין (malshín, “informer”), from the root of לָשׁוֹן (lashón, “tongue”). Cognate with Portuguese malsim, which is even rarer.