Antonyms for the phrase "give stamp of approval give the go-ahead" could include terms like disapproval, rejection, disavowal, or dissent. These words suggest a lack of support, agreement, or validation for a particular action or decision. For instance, if someone proposed a new project, but it did not receive the stamp of approval, they might encounter resistance or difficulty in pursuing it further. Alternatively, if someone gave the go-ahead for a plan, but others in the group dissented, it could create tension and disagreement. Ultimately, the language we use can have a powerful impact on the success or failure of our endeavors.