sinister

UK: /ˈsɪnɪstə^r/ US: /ˈsɪnəstɚ/ ,(sin′ə stər)

WordReference Random House Learner's Dictionary of American English © 2026

sin•is•ter /ˈsɪnəstɚ/   adj. 

1. threatening or suggesting evil, harm, or trouble:
   a sinister face.
2. evil:
   the dictator's sinister purposes.

WordReference Random House Unabridged Dictionary of American English © 2026

sin•is•ter  (sin′ə stər), adj. 

1. threatening or portending evil, harm, or trouble;
   ominous:
   a sinister remark.
2. bad, evil, base, or wicked;
   fell:
   his sinister purposes.
3. unfortunate;
   disastrous;
   unfavorable:
   a sinister accident.
4. of or on the left side;
   left.
5. Heraldry noting the side of an escutcheon or achievement of arms that is to the left of the bearer (opposed to dexter).

• Latin: on the left hand or side, hence unfavorable, injurious
• late Middle English 1375–1425

sin′is•ter•ly, adv. 
sin′is•ter•ness, n. 
Synonyms

• 1. inauspicious, portentous.
• 3. unlucky.

Antonyms

• 1. benign.
• 3. favorable.

Collins Concise English Dictionary © HarperCollins Publishers::

sinister / ˈsɪnɪstə/ adjective

1. threatening or suggesting evil or harm; ominous: a sinister glance
2. evil or treacherous, esp in a mysterious way
3. (usually postpositive) of, on, or starting from the left side from the bearer's point of view and therefore on the spectator's right
4. located on the left side

Compare (for senses 3, 4) dexter1Etymology: 15th Century: from Latin sinister on the left-hand side, considered by Roman augurs to be the unlucky one

ˈsinisterly adverb

ˈsinisterness noun