Break neck is an idiomatic expression used to describe something that is done at a very fast pace or with great haste. The phrase often alludes to the danger of an action, hinting that it could result in harm or disaster. The antonym of break neck, therefore, would be something that is done slowly or at a relaxed pace, without causing any undue risks or harm. Synonyms for this opposite action might include 'deliberate,' 'careful,' 'methodical,' 'cautious,' or 'leisurely.' When it comes to decision-making, antonyms might include 'tentative,' 'considerate,' and 'thoughtful.' In any case, the opposite of break neck is the ease and caution that come with taking things slowly and steadily.