threatening vs sinister

threatening and sinister both are adjectives.

Word	Noun	Adjective	Verb	Adverb
threatening	No	Yes	No	No
sinister	No	Yes	No	No

As adjectives, threatening and sinister are synonyms defined as:

threatening and sinister: threatening or foreshadowing evil or tragic developments

Other synonyms of threatening include baleful, forbidding, menacing, minacious, minatory, ominous.

threatening (adjective)	sinister (adjective)
threatening or foreshadowing evil or tragic developments	threatening or foreshadowing evil or tragic developments
darkened by clouds	stemming from evil characteristics or forces; wicked or dishonorable
	on or starting from the wearer's left