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sinister

[sin-uh-ster]
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adjective
  1. threatening or portending evil, harm, or trouble; ominous: a sinister remark.
  2. bad, evil, base, or wicked; fell: his sinister purposes.
  3. unfortunate; disastrous; unfavorable: a sinister accident.
  4. of or on the left side; left.
  5. Heraldry. noting the side of an escutcheon or achievement of arms that is to the left of the bearer (opposed to dexter).

Origin of sinister

1375–1425; late Middle English < Latin: on the left hand or side, hence unfavorable, injurious
Related formssin·is·ter·ly, adverbsin·is·ter·ness, nounun·sin·is·ter, adjectiveun·sin·is·ter·ly, adverbun·sin·is·ter·ness, noun

Synonyms

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1. inauspicious, portentous. 3. unlucky.

Antonyms

1. benign. 3. favorable.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for sinisterness

sinister

adjective
  1. threatening or suggesting evil or harm; ominousa sinister glance
  2. evil or treacherous, esp in a mysterious way
  3. (usually postpositive) heraldry of, on, or starting from the left side from the bearer's point of view and therefore on the spectator's right
  4. archaic located on the left side
  5. archaic (of signs, omens, etc) unfavourable
Compare dexter 1
Derived Formssinisterly, adverbsinisterness, noun

Word Origin

C15: from Latin sinister on the left-hand side, considered by Roman augurs to be the unlucky one
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for sinisterness

sinister

adj.

early 15c., "prompted by malice or ill-will, intending to mislead," from Old French senestre, sinistre "contrary, false; unfavorable; to the left" (14c.), from Latin sinister "left, on the left side" (opposite of dexter), of uncertain origin. Perhaps meaning properly "the slower or weaker hand" [Tucker], but Klein and Buck suggest it's a euphemism (see left (adj.)) connected with the root of Sanskrit saniyan "more useful, more advantageous." With contrastive or comparative suffix -ter, as in dexter (see dexterity).

The Latin word was used in augury in the sense of "unlucky, unfavorable" (omens, especially bird flights, seen on the left hand were regarded as portending misfortune), and thus sinister acquired a sense of "harmful, unfavorable, adverse." This was from Greek influence, reflecting the early Greek practice of facing north when observing omens. In genuine Roman auspices, the augurs faced south and left was favorable. Thus sinister also retained a secondary sense in Latin of "favorable, auspicious, fortunate, lucky."

Meaning "evil" is from late 15c. Used in heraldry from 1560s to indicate "left, to the left." Bend (not "bar") sinister in heraldry indicates illegitimacy and preserves the literal sense of "on or from the left side" (though in heraldry this is from the view of the bearer of the shield, not the observer of it).

Online Etymology Dictionary, © 2010 Douglas Harper

sinisterness in Medicine

sinister

(sĭnĭ-stər)
adj.
  1. Presaging trouble; ominous.
  2. On the left side; left.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.