The Collaborative International Dictionary of English v.0.48:

Sinister \Sin"is*ter\ (s[i^]n"[i^]s*t[~e]r; 277), a.

   Note: [Accented on the middle syllable by the older poets, as
         Shakespeare, Milton, Dryden.] [L. sinister: cf. F.
         sinistre.]
   1. On the left hand, or the side of the left hand; left; --
      opposed to dexter, or right. "Here on his sinister
      cheek." --Shak.
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            My mother's blood
            Runs on the dexter cheek, and this sinister
            Bounds in my father's                 --Shak.
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   Note: In heraldy the sinister side of an escutcheon is the
         side which would be on the left of the bearer of the
         shield, and opposite the right hand of the beholder.
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   2. Unlucky; inauspicious; disastrous; injurious; evil; -- the
      left being usually regarded as the unlucky side; as,
      sinister influences.
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            All the several ills that visit earth,
            Brought forth by night, with a sinister birth. --B.
                                                  Jonson.
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   3. Wrong, as springing from indirection or obliquity;
      perverse; dishonest; corrupt; as, sinister aims.
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            Nimble and sinister tricks and shifts. --Bacon.
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            He scorns to undermine another's interest by any
            sinister or inferior arts.            --South.
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            He read in their looks . . . sinister intentions
            directed particularly toward himself. --Sir W.
                                                  Scott.
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   4. Indicative of lurking evil or harm; boding covert danger;
      as, a sinister countenance.
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   Bar sinister. (Her.) See under Bar, n.

   Sinister aspect (Astrol.), an appearance of two planets
      happening according to the succession of the signs, as
      Saturn in Aries, and Mars in the same degree of Gemini.

   Sinister base, Sinister chief. See under Escutcheon.
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