sinister
adjective /ˈsɪnɪstə(r)/
  /ˈsɪnɪstər/
- seeming evil or dangerous; making you think something bad will happen
- There was something cold and sinister about him.
 - There is another, more sinister, possibility.
 - We needn’t assume that there was a sinister motive for what she did.
 
Extra Examples- I found his silence rather sinister.
 - There was a sinister undertone in his words.
 
Oxford Collocations Dictionaryverbs- be
 - look
 - seem
 - …
 
- extremely
 - fairly
 - very
 - …
 
Word Originlate Middle English (in the sense ‘malicious, underhand’): from Old French sinistre or Latin sinister ‘left’.