This is the 12027th most frequent Russian word.
злословить
To speak ill or maliciously about someone.
The verb 'злословить' here means to speak maliciously or to gossip meanly, showing disapproval of someone's habit.
Она любит злословить обо всех своих коллегах.
She enjoys speaking maliciously about all her colleagues.
In this instance, 'злословить' is used in a general statement to express an ethical judgment about badmouthing.
Злословить о человеке за его спиной — это некрасиво.
It is unbecoming to speak maliciously about a person behind their back.
Here, 'злословить' indicates that the people spoke ill about someone motivated by a specific event.