I. ˈsinə̇stə(r), chiefly archaic sə̇ˈnis- adjective
Etymology: Middle English sinistre, from Latin sinister left, on the left side, awkward, injurious, evil, unlucky, inauspicious
1. archaic : ominous of evil or wrongdoing : unfavorable , prejudicial
2. obsolete : conveying misleading or detrimental opinion or advice
the sinister application of the malicious, ignorant, and base interpreter — Ben Jonson
3. archaic : dishonestly underhanded : fraudulent
nimble and sinister tricks and shifts — Francis Bacon
4. : evil or productive of evil : bad , corruptive
the sinister character of the early factory system — Walter Lippmann
emotions long repressed sometimes find sinister outlets — V.L.Parrington
the scheme of some sinister intelligence bent on punishing him — Thomas Hardy
critics who … exaggerate the sinister influence of a kind of underworld of economic werewolves — F.L.Mott
denouncing the sinister aims and wicked conduct of those in high places — C.L.Becker
5.
a. : of, relating to, or situated to the left or on the left side of something
was placed on … the sinister side of the church — J.A.Davison
on a helmet, a wreath with the crest, a dexter and a sinister hand proper, grasping a two-handed sword argent — F.W.Steer
specifically : of or relating to the side of a heraldic shield or escutcheon at the left of the bearer
a theory that the bearings of a person who fled … could be assumed and borne in a sinister quarter — F.P.Barnard
b. : of ill omen by reason of being on the left
the victor eagle, whose sinister flight retards our host — Alexander Pope
6. : presaging ill fortune or trouble : portentous , ominous
everything in the room had a new significance, a sinister meaning — G.D.Brown
something devilish and sinister about the whole business — Lewis Mumford
or, more sinister still, the black fog full of birds — Listener
a sinister brightness — a poisonous, threatening flash of pigment, set off by the blackness of the shadows — William Beebe
with a somewhat sinister haircut, a unique black beard that would mark him as a dangerous man — Harrison Smith
7. : accompanied by or leading to disaster or unfavorable developments
expressed their alarm over the sinister results that had followed — W.H.Lawrence
was a sinister idea from the beginning, a surefire recipe for civil war — Edmond Taylor
II. adverb
: to or toward the left
the flag was criticized because the eagle faced sinister , that is, to its own left — Elizabeth W. King