From Longman Dictionary of Contemporary Englishfalse move/stepfalse move/stepa small movement or action that will result in harm One false move and you’re dead. → false
Examples from the Corpus
false move/step• A false step, a forgotten detail.• One false step and we would be down there too.• Leicester are the sporting equivalent of those brave landmine engineers who operate in areas where one false move can destroy everything.• Risking a false step in the bog, she sped over the path.• One false move in the conduct of the attack will spell certain doom for White.• No regrets, no hesitation; there were no false moves left in me.• Any false starts or false moves will result in error and the telltale bugs.• And marriage, I should have thought, is a false step you must have been well warned against. 