from Wiktionary, Creative Commons Attribution/Share-Alike License

An adaptation of the Ancient Greek ψιθύρισµα (psithurisma) or ψιθυρισµός (psithurismos), from ψιθυρίζω (psithurizō, "I whisper"), from ψίθυρος (psithuros, "whispering”, “slanderous").