early 15c., sinistre, "prompted by malice or ill-will; false, dishonest, intending to mislead," with suggestion, report, etc., from Old French senestre, sinistre "contrary, false; unfavorable; to the left" (14c.), from Latin sinister "left, on the left side" (opposite of dexter), a word of uncertain origin. Perhaps meaning properly "the slower or weaker hand" [Tucker], but Klein and Buck suggest it's a euphemism (see left (adj.)) and connected with the root of Sanskrit saniyan "more useful, more advantageous." With contrastive or comparative suffix -ter, as in dexter (see dexterity).
The Latin word was used in augury in the sense of "unlucky, unfavorable" (omens, especially bird flights, seen on the left hand were regarded as portending misfortune), and thus sinister acquired a sense of "harmful, unfavorable, adverse." This was from Greek influence, reflecting the early Greek practice of facing north when observing omens. In genuine Roman auspices, the augurs faced south and left was favorable. Thus sinister also retained a secondary sense in Latin of "favorable, auspicious, fortunate, lucky."
In reference to persons, "deceitful, perfidious," from late 15c. The classical literal sense of "left as opposed to right, in the left side (of the body)" is attested in English from c. 1500. In heraldry (from 1560s) sinister indicates "left, to the left." Related: Sinisterly; sinisterness.
Bend sinister (not bar sinister) in heraldry indicates illegitimacy and preserves the literal sense of "on or from the left side" (though in heraldry this is from the view of the bearer of the shield, not the observer of it; see bend (n.2)).
early 15c., sinistralle, "unlucky, adverse" (a sense now obsolete), from Old French senestral, sinistral or Medieval Latin *sinistralis, from Latin sinister "left, on the left side" (see sinister). The meaning "on, of, or pertaining to the left side" is from 1803. Of persons, "left-handed," by 1904. Related: Sinistrally; sinistrality.
"turned or turning to the left," 1839, a word wanted by the botanists to describe the direction of spiral structures in nature, from Latin sinistrorsus "toward the left side," from sinister "left" (see sinister) + versus "turned," past participle of vertere "to turn" (from PIE root *wer- (2) "to turn, bend").
By 1837 in French. It was paired with dextrorse, but confusion over what was the proper point of view to reckon leftward or rightward spiraling (the observer or the observed) prevented the word being as useful as it might have been. The earlier adjective was sinistrorsal (by 1823).
c. 1200, "opposite of right," probably from Kentish and northern English forms of Old English *lyft "weak; foolish" (in lyft-adl "lameness, paralysis"). Compare East Frisian luf, Dutch dialectal loof "weak, worthless").
Sense of "opposite of right" is from the left being usually the weaker hand), a derived sense also found in cognate Middle Dutch and Low German luchter, luft. Compare Lithuanian kairys "left" and Lettish kreilis "left hand" both from a root that yields words for "twisted, crooked."
The usual Old English winstre/winestra "left" (adj.); "left hand," literally "friendlier," a euphemism used superstitiously to avoid invoking the unlucky forces connected with the left side (compare sinister). The Kentish word itself might have been originally a taboo replacement, if instead it represents PIE *laiwo- "considered conspicuous" (represented in Greek laios, Latin laevus, and Russian levyi). Greek also uses a euphemism for "left," aristeros "the better one" (compare also Avestan vairyastara- "to the left," from vairya- "desirable").
Meaning "being on the left-hand side" is from c. 1300. As an adverb from early 14c. For political senses, see left (n.). Used at least since c. 1600 in various senses of "irregular, illicit;" earlier proverbial sense was "opposite of what is expressed" (mid-15c.), for example over the left (shoulder) "not at all," added to a statement to negate or neglect what was just said (1705). To have two left feet "be clumsy" is attested by 1902.
Phrase out in left field "out of touch with pertinent realities" is attested from 1944, from the baseball fielding position that tends to be far removed from the play (left field in baseball attested by 1867; the fielding positions are from the point of view of the batter). The Parisian Left Bank (of the River Seine) has been associated with intellectual and artistic culture at least since 1893; Left Coast "Pacific Coast of the U.S." is by 1980s.
German link, Dutch linker "left" are said to be not directly related to these, being instead from Old High German slinc and Middle Dutch slink "left," related to Swedish linka "limp," slinka "dangle," and Old English slincan "crawl" (Modern English slink).
1520s, "mystical interpretation of the Old Testament," later "an intriguing society, a small group meeting privately" (1660s), from French cabal, which had both senses, from Medieval Latin cabbala (see cabbala). Popularized in English 1673 as an acronym for five intriguing ministers of Charles II (Clifford, Arlington, Buckingham, Ashley, and Lauderdale), which gave the word its sinister connotations.
c. 1600, "one who studies and resolves cases of conscience," from French casuiste (17c.) or Spanish casuista (the French word also might be from Spanish), Italian casista, all from Latin casus "case" (see case (n.1)) in its Medieval Latin sense "case of conscience." Often since 17c. in a sinister or contemptuous sense "over-subtle reasoner, sophist." Related: Casuistic; casuistical; casuistically.
also saltier, c. 1400, sautour, an ordinary that resembles a St. Andrew's Cross on a shield or flag, consisting of a bend dexter and a bend sinister crossing each other, from Old French sautoir, sautour, literally "stirrup," and directly from Medieval Latin saltarium, noun use of neuter of Latin saltatorius "pertaining to leaping," from salire "to leap" (see salient (adj.)). The connection between stirrups and the diagonal cross is said to be the two deltoid shapes that comprise the cross.