Definition of sinister

• a. - On the left hand, or the side of the left hand; left; -- opposed to dexter, or right.
• a. - Unlucky; inauspicious; disastrous; injurious; evil; -- the left being usually regarded as the unlucky side; as, sinister influences.
• a. - Wrong, as springing from indirection or obliquity; perverse; dishonest; corrupt; as, sinister aims.
• a. - Indicative of lurking evil or harm; boding covert danger; as, a sinister countenance.