Merriam-Webster's Word of the Day for September 30, 2025 is "impetuous." It is an adjective that means acting without thought. "Impetuous" is a synonym for "impulsive." The word can describe a person or an action. For example, an impetuous decision can have serious consequences. The provided example illustrates someone taking an impetuous trip for self-understanding. Impetuous individuals tend to make rash choices, likened to leaping before looking. The origin of "impetuous" lies in the Latin word "impetus," meaning "impulse" or "driving force." This Latin root also gave rise to the English word "impetus." Therefore, "impetuous" essentially describes a forceful, unthinking drive to act.