adj. 25B6; adjective INSIGHTFUL, discerning, sensitive, intuitive, observant; piercing, penetrating, percipient, perspicacious, penetrative, clear-sighted, far-sighted, intelligent, clever, canny, keen, sharp, sharp-witted, astute, shrewd, quick, smart, acute, discriminating; informal on the ball; N. Amer. informal heads-up.
obtuse.