adj. 25B6; adjective DISCERNING, shrewd, perceptive, astute, penetrating, observant, percipient, sharp-witted, sharp, smart, alert, clear-sighted, far-sighted, acute, clever, canny, intelligent, insightful, wise, sage, sensitive, intuitive, understanding, aware, discriminating; informal on the ball; N. Amer. informal heads-up.
stupid.