Tread lightly is an expression that means to be careful and cautious in one's actions. It can be used as a warning to someone to be aware of their surroundings and to not take any unnecessary risks. The crossword solution for this term is 'TIPTOE, ' which is an action that requires one to be light on their feet and to move slowly and carefully. Tiptoeing is often associated with being quiet and stealthy, which is why it is a fitting solution for the term 'tread lightly.'