sinister vs ominous

sinister and ominous both are adjectives.

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

As adjectives, sinister and ominous are synonyms defined as:

sinister and ominous: threatening or foreshadowing evil or tragic developments

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

sinister (adjective)	ominous (adjective)
threatening or foreshadowing evil or tragic developments	threatening or foreshadowing evil or tragic developments
stemming from evil characteristics or forces; wicked or dishonorable	presaging ill fortune
on or starting from the wearer's left