adj. 25B6; adjective SHREWD, astute, smart, sharp, sharp-witted, discerning, penetrating, discriminating, perceptive, perspicacious, wise, sagacious; cunning, crafty, wily; N. Amer. as sharp as a tack; informal savvy; Brit. informal suss, sussed; N. Amer. informal heads-up; dated long-headed; rare argute.
foolish.