adj. 1 suggestive of evil; looking malignant or villainous. 2 wicked or criminal (a sinister motive). 3 of evil omen. 4 Heraldry of or on the left-hand side of a shield etc. (i.e. to the observer's right). 5 archaic left-hand. sinisterly adv. sinisterness n.
[ ME f. OF sinistre or L sinister left ]