Antonyms for the phrase "give the go-ahead" include "reject," "prohibit," "disapprove," "deny," "forbid," "oppose," "hold back," "delay," "inhibit," and "withhold." These words imply different levels of disapproval or reluctance towards proceeding with a particular action. Whereas "reject" indicates a complete opposition to an idea or plan, "delay" suggests a willingness to revisit the issue at a later time. Similarly, "disapprove" implies a lack of enthusiasm, while "withhold" suggests the decision to hold off on giving approval. Overall, antonyms for "give the go-ahead" offer a range of negative options to consider when decision-making.