Treacherous/ˈtretʃərəs/ Definition 1 of 3Pro Tip 1/3Hidden Dangers Use it when something appears safe but has risks that are not obvious. The calm sea is treacherous to swim in due to strong undercurrents. Pro Tip 2/3Extreme Conditions Often used to describe challenging natural conditions like weather or terrain. The treacherous ice storm made the roads impassable. Pro Tip 3/3Difficulty Level Suggests a high level of difficulty or challenge in navigating a situation. The negotiations were treacherous, with many potential pitfalls.