shrewd

Synonyms: acute argute artful astucious astute brainy cagey calculating canny crafty cunning cutting deep discerning discriminating farsighted foxy heady ingenious inside in the know judicious keen knowing on the inside on top of penetrating perceptive perspicacious piercing probing profound prudent quickwitted sagacious savvy sensible shark sharp slick slippery sly smart smooth streetwise tricky underhand up on wily wise wised up

Antonyms: foolish frivolous naive stupid unthinking