Dictionary.com Unabridged (v 1.1) - Cite This Source - Share This

American Heritage Dictionary - Cite This Source - Share This

sin·is·ter       (sĭn'ĭ-stər)  Pronunciation Key  adj.   Suggesting or threatening evil: a sinister smile. Presaging trouble; ominous: sinister storm clouds. Attended by or causing disaster or inauspicious circumstances. On the left side; left. Heraldry Situated on or being the side of a shield on the wearer's left and the observer's right. [Middle English sinistre, unfavorable, from Old French, from Latin sinister, on the left, unlucky.] sin'is·ter·ly adv., sin'is·ter·ness n. Synonyms: These adjectives apply to what is indicative of or threatens great harm, disaster, or evil. Sinister usually implies impending or lurking danger that makes its presence felt by ominous signs or portents: We heard a sinister laugh from behind the door. Baleful intensifies the sense of menace; it suggests a deadly, virulent, or poisonous quality: The guard's baleful glare frightened the children. Malign applies to what manifests an evil disposition, nature, influence, or intent: "The Devil . . . with jealous leer malign/Eyed them askance" (John Milton).

Online Etymology Dictionary - Cite This Source - Share This
sinister 

WordNet - Cite This Source - Share This

sinister
adjective
1.	threatening or foreshadowing evil or tragic developments; "a baleful look"; "forbidding thunderclouds"; "his tone became menacing"; "ominous rumblings of discontent"; "sinister storm clouds"; "a sinister smile"; "his threatening behavior"; "ugly black clouds"; "the situation became ugly" [syn: baleful]
2.	stemming from evil characteristics or forces; wicked or dishonorable; "black deeds"; "a black lie"; "his black heart has concocted yet another black deed"; "Darth Vader of the dark side"; "a dark purpose"; "dark undercurrents of ethnic hostility"; "the scheme of some sinister intelligence bent on punishing him"-Thomas Hardy [syn: black]
3.	on or starting from the wearer's left; "bar sinister"

American Heritage Stedman's Medical Dictionary - Cite This Source - Share This

sinister sin·is·ter (sĭn'ĭ-stər)
adj.

1. Presaging trouble; ominous.
2. On the left side; left.

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sin'is·ter·ly adv.
sin'is·ter·ness n.

Webster's Revised Unabridged Dictionary - Cite This Source - Share This

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.

My mother's blood Runs on the dexter cheek, and this sinister Bounds in my father's --Shak.

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.

2. Unlucky; inauspicious; disastrous; injurious; evil; -- the left being usually regarded as the unlucky side; as, sinister influences.

All the several ills that visit earth, Brought forth by night, with a sinister birth. --B. Jonson.

3. Wrong, as springing from indirection or obliquity; perverse; dishonest; corrupt; as, sinister aims.

Nimble and sinister tricks and shifts. --Bacon.

He scorns to undermine another's interest by any sinister or inferior arts. --South.

He read in their looks . . . sinister intentions directed particularly toward himself. --Sir W. Scott.

4. Indicative of lurking evil or harm; boding covert danger; as, a sinister countenance.

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.