The Collaborative International Dictionary of English v.0.48:

Shrewd \Shrewd\, a. [Compar. Shrewder; superl. Shrewdest.]
   [Originally the p. p. of shrew, v.t.]
   1. Inclining to shrew; disposing to curse or scold; hence,
      vicious; malicious; evil; wicked; mischievous; vexatious;
      rough; unfair; shrewish. [Obs.] --Chaucer.
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            [Egypt] hath many shrewd havens, because of the
            great rocks that ben strong and dangerous to pass
            by.                                   --Sir J.
                                                  Mandeville.
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            Every of this happy number
            That have endured shrewd days and nights with us.
                                                  --Shak.
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   2. Artful; wily; cunning; arch.
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            These women are shrewd tempters with their tongues.
                                                  --Shak.
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   3. Able or clever in practical affairs; sharp in business;
      astute; sharp-witted; sagacious; keen; as, a shrewd
      observer; a shrewd design; a shrewd reply.
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            Professing to despise the ill opinion of mankind
            creates a shrewd suspicion that we have deserved it.
                                                  --Secker.
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   Syn: Keen; critical; subtle; artful; astute; sagacious;
        discerning; acute; penetrating.

   Usage: Shrewd, Sagacious. One who is shrewd is keen to
          detect errors, to penetrate disguises, to foresee and
          guard against the selfishness of others. Shrewd is a
          word of less dignity than sagacious, which implies a
          comprehensive as well as penetrating mind, whereas
          shrewd does not.
          [1913 Webster] -- Shrewd"ly, adv. -- Shrewd"ness,
          n.
          [1913 Webster]

WordNet (r) 3.0 (2006):

shrewdness
    n 1: intelligence manifested by being astute (as in business
         dealings) [syn: shrewdness, astuteness, perspicacity,
         perspicaciousness]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "shrewdness":
   Italian hand, acumen, acuteness, animal cunning, art, artfulness,
   artifice, astuteness, cageyness, callidity, canniness, cleverness,
   craft, craftiness, cunning, cunningness, deviousness, discernment,
   discrimination, fine Italian hand, finesse, foxiness, gamesmanship,
   guile, guilefulness, ingeniousness, insidiousness, inventiveness,
   keenness, low cunning, one-upmanship, pawkiness, penetration,
   percipience, perspicacity, readiness, resourcefulness,
   satanic cunning, sharpness, shiftiness, slickness, slipperiness,
   slyness, sneakiness, sophistry, stealth, stealthiness, subtility,
   subtilty, subtleness, subtlety, suppleness, trickiness, wariness,
   wiles, wiliness, wit