Slander was a term for spoken defamation.
In 2155, the Coridanite ambassador described Tellarite claims that the Orions were attacking their Tellarite freighters as slander.
In 2268, after Sarek made disparaging remarks that implied Tellarites were involved in illegal activities, Gav threatened the Vulcan, saying he would pay for his slander. (TOS: "Journey to Babel")
In 2369, after Doctor Reyga accused Kurak of sabotaging the metaphasic shield, the Klingon told Reyga not to continue slandering him or he would pay. (TNG: "Suspicions")
In 2371, when Odo accused Morka, Bo'rak, and Atul of being spies and saboteurs, Morka accused the Changeling of slander and assured him that, if his family learned of this, they would come to Deep Space 9 and kill Odo. (DS9: "Visionary")
In 2374, Dukat claimed that his name and reputation had been twisted and slandered since the end of the Occupation of Bajor. (DS9: "Waltz")