The antonyms for "out flank" depend on the context and the intended meaning. If "out flank" means to surpass or outdo, the antonyms could be "underachieve," "fail," or "lose." On the other hand, if "out flank" means to attack or ambush, the antonyms could be "retreat, "defend," or "guard." Additionally, if "out flank" implies an unfair or unethical advantage, the antonyms might include "honor," "fairness," or "equity." It is essential to consider the specific meaning intended in the context to identify appropriate antonyms for the term "out flank.