If you say something slanderously, you say something bad about someone that is not true.
Saying things slanderously is very mean and can hurt people's feelings.
Examples:
She spoke slanderously about her friend.
He was accused of speaking slanderously about his boss.
The girl was crying because someone talked about her slanderously.
The cat looked at the dog slanderously.
The dragon spoke slanderously about the knight.
The witch cackled slanderously as she spread rumors.