sinister

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Suggesting or threatening harm or evil.
• adjective Causing or intending harm or evil; wicked.
• adjective Portending misfortune or disaster; ominous.
• adjective Attended by or causing misfortune or disaster.
• adjective Archaic On the left side; left.
• adjective Heraldry Situated on or being the side of a shield on the wearer's left and the observer's right.

from The Century Dictionary.

• Left, as opposed to right; on the left side; specifically, in heraldry, noting the left-hand side of the person who carries the shield on his arm (therefore the right-hand side of the spectator): the sinister part of the escutcheon is opposed to the dexter part (see dexter).
• On or toward the left or unlucky side; hence, of ill omen; inauspicious; threatening or suggesting evil.
• Bringing evil; harmful; malign; unfortunate in results.
• Unpleasant; disagreeable.
• Malicious; evil; base; wrong.

from the GNU version of the Collaborative International Dictionary of English.

• adjective On the left hand, or the side of the left hand; left; -- opposed to dexter, or right.
• adjective Unlucky; inauspicious; disastrous; injurious; evil; -- the left being usually regarded as the unlucky side.
• adjective Wrong, as springing from indirection or obliquity; perverse; dishonest; corrupt.
• adjective Indicative of lurking evil or harm; boding covert danger.
• adjective (Her.) See under Bar, n.
• adjective (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.
• adjective See under Escutcheon.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Inauspicious, ominous, unlucky, illegitimate (as in bar sinister).
• adjective Evil or seemingly evil; indicating lurking danger or harm.
• adjective Of the left side.
• adjective heraldry On the left side of a shield from the wearer's standpoint, and the right side to the viewer.
• adjective obsolete Wrong, as springing from indirection or obliquity; perverse; dishonest.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective stemming from evil characteristics or forces; wicked or dishonorable
• adjective on or starting from the wearer's left
• adjective threatening or foreshadowing evil or tragic developments