"On thin ice" is an idiomatic expression that refers to being in a precarious and risky situation, where the slightest mistake could have serious consequences. There are many synonyms for this phrase, including "walking on a tightrope," "skating on thin ice," "treading on dangerous ground," "in a dangerous position," "playing with fire," and "in a delicate situation." These expressions all convey the idea of being in a risky position, where one false move could result in disaster. So, whether you are walking on thin ice, treading carefully, or playing with fire, it's important to be cautious and aware of the potential consequences of your actions.