WordWeb Online

1. Marked by practical hardheaded intelligence
   "he was too shrewd to go along with them on a road that could lead only to their overthrow";
   - astute, sharp, argute [literary], savvy [informal]
    
2. Serving one's own interests in an unemotional, analytical manner
   "the most shrewd and selfish men in the community";
   - calculating, calculative, conniving, scheming

Derived forms: shrewdest, shrewder

See also: hard, smart