Sagacious comes from the Latin word sagax, meaning “wise” or “perceptive.” In English, it has been used since the 17th century to describe people who have sharp mental discernment and keen practical sense. It is often used to describe people who are shrewd, astute, or perceptive in their dealings with others. Today, sagacious is a common word in English, and is often used to describe people who are wise, intelligent, and insightful.