1. (a.) Evil; ominous; threatening\.

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

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

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

adverse amoral antagonistic apocalyptic backhand backhanded bad baleful baneful base black bodeful boding circuitous conflicting conscienceless contrary corrupt corrupted counter counteractive counterclockwise criminal crooked dark deflectional detrimental deviant deviative devious diabolical difficult digressive dire disastrous dishonest dishonorable divagational divergent doomful doubtful dreary dubious evasive evil evil-starred excursive fateful felonious fishy foreboding fraudulent furtive gloomy hard harmful hostile ill ill-boding ill-fated ill-got ill-gotten ill-omened ill-starred immoral improper in opposition inaccurate inauspicious indirect inexpedient inferior inimical insidious invalid larboard left left-hand left-handed left-wing left-wingish levorotatory liberal lowering malefic maleficent malevolent malicious malign malignant menacing minacious minatory miserable near nefarious nigh not easy not kosher oblique of evil portent ominous opposed opposing opposite peccant pernicious port portending portentous questionable radical rigorous rotten shady shameless shifty side sidelong sinful sinistral sinistrocerebral sinistrocular sinistrogyrate sinistrorse slippery sneaky somber stressful suspicious threatening treacherous tricky troublesome troublous trying unconscienced unconscientious unconscionable underhand underhanded unethical unfavorable unfortunate unhealthy unkind unlucky unpleasant unprincipled unpromising unpropitious unsavory unscrupulous unskillful unstraightforward untoward vicious villainous wicked without remorse without shame wretched wrong