Shrewd, a. [Compar. Shrewder; superl. Shrewdest.] — Webster enters it under “shrewd”
Etymology: [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. [Egypt] hath many shrewd havens, because of the great rocks that ben strong and dangerous to pass by. Sir J. Mandeville. Every of this happy number That have endured shrewd days and nights with us. Shak.
2. Artful; wily; cunning; arch. These women are shrewd tempters with their tongues. Shak.
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. Professing to despise the ill opinion of mankind creates a shrewd suspicion that we have deserved it. Secker.
Syn. -- Keen; critical; subtle; artful; astute; sagacious; discerning; acute; penetrating. -- 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. -- Shrewd"ly, adv. -- Shrewd"ness, n.
Shades of meaning
Fernald has no entry of its own for shrewdness; he lists it under acumen.
Where he writes about it:
Shrewdness is keenness or sagacity, often with a somewhat evil bias, as ready to take advantage of duller intellects. — from acumen
We speak of the acuteness of an observer or a reasoner, the insight and discernment of a student, a clergyman, or a merchant, the sagacity of a hound, the keenness of a debater, the shrewdness of a usurer, the penetration, perspicacity, and acumen of a philosopher. — from acumen