threatening or portending evil, harm, or trouble; ominous

a sinister remark.

bad, evil, base, or wicked; fell

his sinister purposes.

unfortunate; disastrous; unfavorable

a sinister accident.

of or on the left side; left.

Heraldry . noting the side of an escutcheon or achievement of arms that is to the left of the bearer ( opposed to dexter ).

adjective

benevolent , kind , nice

adjective

adverse , apocalyptic , bad , baleful , baneful , blackhearted , corrupt , deleterious , dire , disastrous , dishonest , disquieting , doomful , evil , foreboding , harmful , hurtful , ill-boding , inauspicious , injurious , lowering , malefic , malevolent , malign , malignant , mischievous , obnoxious , ominous , pernicious , perverse , poisonous , portentous , threatening , unfavorable , unfortunate , unlucky , unpropitious , woeful , dark , despicable , devilish , diabolical , forbidding , frightening , grim , left , malicious , menacing , underhand , wicked , wrong