Discernment, n.
Etymology: [Cf. F. discernement.]
1. The act of discerning.
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.
Shades of meaning
Fernald has no entry of its own for discernment; he lists it under acumen, wisdom.
Where he writes about it:
Insight and discernment are applied oftenest to the judgment of character; penetration and perspicacity to other subjects of knowledge. — from acumen
We speak of the acuteness of an observer or a reasoner, the insight and discernment of a student, a clergyman, or a merchant, the sagacity of a hound, the keenness of a debater, the shrewdness of a usurer, the penetration, perspicacity, and acumen of a philosopher. — from acumen