sin·is·ter 
(sĭnĭ-stər)
(sĭnĭ-stər)adj.
1.
a. Suggesting or threatening harm or evil: a sinister smile.
b. Causing or intending harm or evil; wicked: a sinister conspiracy.
2.
a. Portending misfortune or disaster; ominous: sinister storm clouds.
b. Attended by or causing misfortune or disaster: "The day has passed without any sinister accident" (John Quincy Adams).
3.
a. Archaic On the left side; left.
b. 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.]
sinis·ter·ly adv.
sinis·ter·ness n.