The phrase "plight troth" refers to a mutual promise or commitment made between two people. The antonyms, therefore, would be words that signify a lack of commitment or a breaking of a promise. Some antonyms for "plight troth" include betrayal, deception, dishonesty, disloyalty, insincerity, and infidelity. These words convey a sense of unfaithfulness and a breach of trust, which are the opposite of the sincere vow represented by the phrase "plight troth." Using these antonyms in a conversation could indicate a pessimistic view or a distrust of others, while employing "plight troth" denotes an optimistic and open commitment to others.