Definitions of sinister:

• adjective:   on or starting from the wearer's left

  Example: "Bar sinister"

• adjective:   stemming from evil characteristics or forces; wicked or dishonorable

  Example: "The scheme of some sinister intelligence bent on punishing him-Thomas Hardy"

• adjective:   threatening or foreshadowing evil or tragic developments

  Example: "Sinister storm clouds"