Open English Wordnet
(s)baleful, forbidding, menacing, minacious, minatory, ominous, sinister, threateningthreatening 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”