Pronunciation: (sin'u-stur),[key] —adj. 1. threatening or portending evil, harm, or trouble; ominous: a sinister remark. 2. bad, evil, base, or wicked; fell: his sinister purposes. 3. unfortunate; disastrous; unfavorable: a sinister accident. 4. of or on the left side; left.
5. Heraldry.noting the side of an escutcheon or achievement of arms that is to the left of the bearer (opposed to dexter).