[adj] threatening or foreshadowing evil or tragic developments; "a baleful look"; "forbidding thunderclouds"; "his tone became menacing"; "ominous rumblings of discontent"; "sinister storm clouds"; "a sinister smile"; "his threatening behavior"; "ugly black clouds"; "the situation became ugly"
[adj] (heraldry) on or starting from the wearer's left; "bar sinister"
[adj] stemming from evil characteristics or forces; wicked or dishonorable; "black deeds"; "a black lie"; "his black heart has concocted yet another black deed"; "Darth Vader of the dark side"; "a dark purpose"; "dark undercurrents of ethnic hostility"; "the scheme of some sinister intelligence bent on punishing him"-Thomas Hardy
Synonyms
alarming, baleful, black, dark, evil, forbidding, menacing, minacious, minatory, ominous, sinistral, threatening, ugly, wicked