Antonyms for "gave the go-ahead" can range from "halted" to "rejected." "Halted" implies a complete stop of the action or decision, whereas "rejected" means that the idea was not approved at all. Other antonyms could include "delayed," "postponed," "reconsidered," "blocked," or "vetoed." Each of these words represents a different level of approval or disapproval, and understanding their meanings is crucial when looking for ways to express dissent or disagreement. By considering these antonyms, one can better express their opinion on an idea or decision without using the phrase "gave the go-ahead.