Double dealer, a term used to refer to someone who is dishonest, deceptive, or insincere, has several antonyms. The opposite of a double dealer is an honest, truthful, or trustworthy person. Synonyms for double dealer include backstabber, betrayer or a traitor. Antonyms, on the other hand, include loyal, sincere, trustworthy or faithful, indicating that the person does not engage in dishonest activities or betray the trust of others. It is important to identify and avoid double dealers in both personal and professional relationships to maintain integrity and foster healthy relationships built on trust and honesty.