Source : Webster's Revised Unabridged Dictionary (1913)

Acumen \A*cu"men\, n. [L. acumen, fr. acuere to sharpen. Cf.
   {Acute}.]
   Quickness of perception or discernment; penetration of mind;
   the faculty of nice discrimination. --Selden.

   Syn: Sharpness; sagacity; keenness; shrewdness; acuteness.

Source : WordNet®

acumen
     n 1: a tapering point
     2: shrewdness shown by keen insight [syn: {insightfulness}]