"threatening" in the verb sense
1. endanger, jeopardize, jeopardise, menace, threaten, imperil, peril
pose a threat to present a danger to
"The pollution is endangering the crops"
2. threaten
to utter intentions of injury or punishment against
"He threatened me when I tried to call the police"
3. threaten
to be a menacing indication of something
"The clouds threaten rain"
"Danger threatens"
"threatening" in the adjective sense
1. baleful, forbidding, menacing, minacious, minatory, ominous, sinister, threatening
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"
2. heavy, lowering, sullen, threatening
darkened by clouds
"a heavy sky"
Source: WordNet® (An amazing lexical database of English)
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