Fork tongue is a term used to describe someone who is untrustworthy and deceitful. There are several synonyms for this term that can be used, depending on the context. Some common synonyms for fork tongue include double-dealing, duplicitous, two-faced, disingenuous, insincere, and hypocritical. Other synonyms that might be used to describe someone who is untrustworthy include treacherous, deceitful, cunning, and crafty. It's important to choose the right synonym for the situation to ensure that the message is clear and accurate. Whether you're talking about someone who is dishonest or simply unreliable, there are plenty of words that can help you get your point across.