The word co-conspirator implies a person who collaborates with another person to commit a crime or wrongdoing. Therefore, antonyms for this term would be persons who are not involved in any illegal activities or who are totally opposed to such activities. Some antonyms for co-conspirator include ally, helper, friend, supporter, well-wisher, and confidant. Other antonyms can also include rival, opponent, detractor, adversary, nemesis, and enemy. These words imply people who are not involved in any collaborative activities with the person in question and may not share their beliefs, goals or intentions. The use of these antonyms establishes a clear distinction between those who indulge in unlawful activities and those who stand by the principles of justice and morality.