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.
      [1913 Webster]

            [Egypt] hath many shrewd havens, because of the
            great rocks that ben strong and dangerous to pass
            by.                                   --Sir J.
                                                  Mandeville.
      [1913 Webster]

            Every of this happy number
            That have endured shrewd days and nights with us.
                                                  --Shak.
      [1913 Webster]

   2. Artful; wily; cunning; arch.
      [1913 Webster]

            These women are shrewd tempters with their tongues.
                                                  --Shak.
      [1913 Webster]

   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.
      [1913 Webster]

            Professing to despise the ill opinion of mankind
            creates a shrewd suspicion that we have deserved it.
                                                  --Secker.
      [1913 Webster]

   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):

shrewdly
    adv 1: in a shrewd manner; "he invested his fortune astutely";
           "he was acutely insightful" [syn: astutely, shrewdly,
           sagaciously, sapiently, acutely]