The antonyms for the word "more undissembling" would be words like dishonest, insincere, deceitful, and untruthful. These antonyms describe people who are not open or transparent in their behavior and communications. They are known for covering up the truth, misleading others, and behaving in a secretive manner. People who exhibit these qualities often have hidden agendas and are not trustworthy in their interactions. In contrast, individuals who are more undissembling are candid, direct, and forthright in their communication style. They are known for their transparency and honesty, making them reliable and trustworthy individuals to do business with.