Merriam-Webster Collegiate Dictionary - shrewd

 adjective  Etymology: Middle English shrewed, from shrewe + 1-ed  Date: 13th century  1. archaic mischievous  2. obsolete abusive, shrewish  3. obsolete ominous, dangerous  4.  a. severe, hard a ~ knock  b. sharp, piercing a ~ wind  5.  a. marked by clever discerning awareness and hardheaded acumen ~ common sense  b. given to wily and artful ways or dealing a ~ operator  • ~ly adverb  • ~ness noun Synonyms:  ~, sagacious, perspicacious, astute mean acute in perception and sound in judgment. ~ stresses practical, hardheaded cleverness and judgment a ~ judge of character. sagacious suggests wisdom, penetration, and farsightedness sagacious investors got in on the ground floor. perspicacious implies unusual power to see through and understand what is puzzling or hidden a perspicacious counselor saw through the child's facade. astute suggests ~ness, perspicacity, and diplomatic skill an astute player of party politics.