WordNet sense 1 (possessing sound knowledge):

well-informed

WordNet sense 2 (having or appealing to those having worldly knowledge and refinement and savoir-faire):

sophisticated

WordNet sense 3 (exercising or showing good judgment):

healthy, levelheaded, sound, level-headed

WordNet sense 4 (showing reason or sound judgment):

reasonable, sensible

WordNet sense 5 (endowed with the capacity to reason):

reasoning, thinking

WordNet sense 6 (consistent with or based on or using reason):

rational

WordNet sense 7 (apprehending and responding with speed and sensitivity):

quick, ready

WordNet sense 8 (characterized by quickness and ease in learning):

bright, smart

WordNet sense 9 (having or marked by unusual and impressive intelligence):

brainy, brilliant

WordNet sense 10 (mentally quick and resourceful):

apt, clever

WordNet sense 11 (mentally responsive):

alert