Merriam-Webster Collegiate Dictionary - sinister

 adjective  Etymology: Middle English sinistre, from Anglo-French senestre on the left, from Latin sinistr-, ~ on the left side, unlucky, inauspicious  Date: 15th century  1. archaic unfavorable, unlucky  2. archaic fraudulent  3. singularly evil or productive of evil  4.  a. of, relating to, or situated to the left or on the left side of something; especially being or relating to the side of a heraldic shield at the left of the person bearing it  b. of ill omen by reason of being on the left  5. presaging ill fortune or trouble  6. accompanied by or leading to disaster  • ~ly adverb  • ~ness noun Synonyms:  ~, baleful, malign mean seriously threatening evil or disaster. ~ suggests a general or vague feeling of fear or apprehension on the part of the observer a ~ aura haunts the place. baleful imputes perniciousness or destructiveness to something whether working openly or covertly exerting a corrupt and baleful influence. malign applies to what is inherently evil or harmful the malign effects of racism.