The twelfth arcanum is about the word used deliberately to wound. An insult in front of witnesses, a rumour set going in order to do damage, mockery of something a person cannot change.
In the lineage this comes back as talk behind one's back. What is said about the descendant is not what is actually so; misunderstandings arise out of second-hand retelling; conflicts flare up in words and drag on for years, though the whole thing came down to a single sentence. Often the person has a sharp tongue of their own, one they are proud of — and does not connect the two.
The working-off is to watch one's speech where nobody will check it. Not to take part in a conversation about a person who is not there; not to answer blow with blow in words; to apologise for what was said, even if years have passed and the occasion seems trivial. What works this law off is not silence but the choice of words.