The term "gave stamp of approval" implies an endorsement or approval of something. Therefore, antonyms for this phrase would be disapproval or rejection. If someone does not give their stamp of approval, it means that they have not endorsed or approved of the matter at hand. In contrast, if someone gives their stamp of disapproval, they have explicitly rejected or disapproved of the matter. Other antonyms for "gave stamp of approval" may include condemn, criticize, rebuke, denounce, or oppose, among others. These words represent opposite meanings to giving an endorsement, demonstrating dissatisfaction or negative feedback.