Penetration, n.
Etymology: [L. penetratio: cf. F. pénétration.]
1. The act or process of penetrating, piercing, or entering; also, the act of mentally penetrating into, or comprehending, anything difficult. And to each in ward part, With gentle penetration, though unseen, Shoots invisible virtue even to the deep. Milton. A penetration into the difficulties of algebra. Watts.
2. Acuteness; insight; sharp discoverment; sagacity; as, a person of singular penetration. Walpole.
Syn. -- Discernment; sagacity; acuteness; sharpness; discrimination. See Discernment, and Sagacity.
Shades of meaning
Fernald has no entry of its own for penetration; he lists it under acumen, entrance.
Where he writes about it:
Sharpness, acuteness, and insight, however keen, and penetration, however deep, fall short of the meaning of acumen, which implies also ability to use these qualities to advantage. — from acumen
There are persons of keen insight and great penetration to whom these powers are practically useless. — from acumen
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