sinister

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Suggesting or threatening evil: a sinister smile.
2. adj. Presaging trouble; ominous: sinister storm clouds.
3. adj. Attended by or causing disaster or inauspicious circumstances.
4. adj. On the left side; left.
5. adj. Heraldry Situated on or being the side of a shield on the wearer's left and the observer's right.

Century Dictionary and Cyclopedia

1. 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). Bearings such as beasts and birds nearly always turn away from the sinister and toward the dexter; when they are turned toward the sinister, they are said to be reversed. See cut under point, 21.
2. On or toward the left or unlucky side; hence, of ill omen; inauspicious; threatening or suggesting evil.
3. Bringing evil; harmful; malign; unfortunate in results.
4. Unpleasant; disagreeable.
5. Malicious; evil; base; wrong.

Wiktionary

1. adj. Inauspicious, ominous, unlucky.
2. adj. Evil, seeming to be evil.
3. adj. Of the left side.
4. adj. The left side of a shield from the wearer's standpoint, and the right side to the viewer.

GNU Webster's 1913

1. adj. On the left hand, or the side of the left hand; left; -- opposed to dexter, or right.
2. adj. Unlucky; inauspicious; disastrous; injurious; evil; -- the left being usually regarded as the unlucky side.
3. adj. Wrong, as springing from indirection or obliquity; perverse; dishonest; corrupt.
4. adj. Indicative of lurking evil or harm; boding covert danger.

WordNet 3.0

1. adj. stemming from evil characteristics or forces; wicked or dishonorable
2. adj. on or starting from the wearer's left
3. adj. threatening or foreshadowing evil or tragic developments