WordWeb Online

1. Unobtrusively perceptive and sympathetic
   "a discerning editor";
   - discreet
    
2. Quick to understand
   "a kind and discerning friend";
   - apprehensive
    
3. Able to make or detect effects of great subtlety; sensitive
   "discerning taste"; "a discerning eye for colour"
    
4. Having or revealing keen insight and good judgment
   "a discerning critic"; "a discerning reader"

1. See or hear differences; identify a particular part or parts of a whole; detect with difficulty
   - spot, recognize, recognise [Brit], distinguish, pick out, make out, tell apart
    
2. Perceive, recognize, or understand

See also: clear, clear-eyed, clear-sighted, critical, discriminating, perceptive, percipient, perspicacious, prescient, tactful

Antonym: undiscerning