threatening or foreshadowing evil or tragic developments
e.g. a baleful look
e.g. forbidding thunderclouds
e.g. his tone became menacing
e.g. ominous rumblings of discontent
e.g. sinister storm clouds
e.g. a sinister smile
e.g. his threatening behavior
e.g. ugly black clouds
e.g. the situation became ugly
Synonym: forbidding menacing minacious minatory ominous sinister threatening