The Collaborative International Dictionary of English v.0.48:

Discernment \Dis*cern"ment\, n. [Cf. F. discernement.]
   1. The act of discerning.
      [1913 Webster]

   2. The power or faculty of the mind by which it distinguishes
      one thing from another; power of viewing differences in
      objects, and their relations and tendencies; penetrative
      and discriminate mental vision; acuteness; sagacity;
      insight; as, the errors of youth often proceed from the
      want of discernment.

   Syn: Judgment; acuteness; discrimination; penetration;
        sagacity; insight. -- Discernment, Penetration,
        Discrimination. Discernment is keenness and accuracy
        of mental vision; penetration is the power of seeing
        deeply into a subject in spite of everything that
        intercepts the view; discrimination is a capacity of
        tracing out minute distinctions and the nicest shades of
        thought. A discerning man is not easily misled; one of a
        penetrating mind sees a multitude of things which escape
        others; a discriminating judgment detects the slightest
        differences.
        [1913 Webster]

WordNet (r) 3.0 (2006):

discernment
    n 1: the cognitive condition of someone who understands; "he has
         virtually no understanding of social cause and effect"
         [syn: understanding, apprehension, discernment,
         savvy]
    2: delicate discrimination (especially of aesthetic values);
       "arrogance and lack of taste contributed to his rapid
       success"; "to ask at that particular time was the ultimate in
       bad taste" [syn: taste, appreciation, discernment,
       perceptiveness]
    3: perception of that which is obscure [syn: discernment,
       perceptiveness]
    4: the mental ability to understand and discriminate between
       relations [syn: sagacity, sagaciousness, judgment,
       judgement, discernment]
    5: the trait of judging wisely and objectively; "a man of
       discernment" [syn: discretion, discernment]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "discernment":
   acuity, acumen, acuteness, apperception, astuteness, clear sight,
   cogency, color vision, cone vision, critical discernment,
   day vision, daylight vision, discrimination, eye, eye-mindedness,
   eyesight, farseeingness, farsight, farsightedness, field of view,
   field of vision, flair, foresight, foresightedness, horizon,
   incisiveness, insight, intuition, judgment, keen sight, keenness,
   ken, longheadedness, longsightedness, night vision, penetration,
   perception, perceptiveness, percipience, peripheral field,
   peripheral vision, perspicaciousness, perspicacity, perspicuity,
   perspicuousness, photopia, power of sight, providence, purview,
   quick sight, range, reason, rod vision, sagaciousness, sagacity,
   scope, scotopia, seeing, sense of sight, sensibility, shrewdness,
   sight, sightedness, sweep, trenchancy, twilight vision,
   unobstructed vision, vision, visual acuity, visual field,
   visual sense, wit