The antonym of cautious is reckless.
Explanation: The term ‘cautious’ refers to being careful to avoid potential problems or dangers, demonstrating a level of prudence and consideration. On the other hand, ‘reckless’ describes behavior that is not careful and often involves taking risks without considering the consequences. While a cautious person tends to think before acting, a reckless individual often acts impulsively, disregarding safety and forethought.