left:  The Old English word for ‘left’ was winestra. Etymologically this meant ‘friendlier’ (it is related to Swedish vän ‘friend’), and its euphemistic application to ‘left’ is a reminder that historically the left-hand side of the body has been superstitiously regarded as of ill omen. To call it ‘friendly’ (a usage which survives in Swedish vänster and Danish venstre ‘left’) was an attempt to placate the evil forces of the left. (Latin sinister ‘left’ is similarly fraught with negative connotations.
It too had euphemistic origins – it came from a source meaning ‘more useful’ – and it developed the figurative senses ‘unfavourable’, ‘injurious’, etc, taken over and extended by English in sinister .) An ancestor of left existed in Old English – left or *lyft. But it meant ‘weak’ or ‘foolish’, and it was not until the 13th century that it came to be used as the partner of right.
c. 1200, from Kentish and northern English form of Old English lyft- "weak, foolish" (compare lyft-adl "lameness, paralysis," East Frisian luf, Dutch dialectal loof "weak, worthless"). It emerged 13c. as "opposite of right" (the left being usually the weaker hand), a derived sense also found in cognate Middle Dutch and Low German luchter, luft. But German link, Dutch linker "left" are from Old High German slinc and Middle Dutch slink "left," related to Old English slincan "crawl," Swedish linka "limp," slinka "dangle."
Replaced Old English winestra, literally "friendlier," a euphemism used superstitiously to avoid invoking the unlucky forces connected with the left side (see sinister). The Kentish word itself may have been originally a taboo replacement, if instead it represents PIE root *laiwo-, meaning "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"). But Lithuanian kairys "left" and Lettish kreilis "left hand" derive from a root that yields words for "twisted, crooked."
As an adverb from early 14c. As a noun from c. 1200. Political sense arose from members of a legislative body assigned to the left side of a chamber, first attested in English 1837 (by Carlyle, in reference to the French Revolution), probably a loan-translation of French la gauche (1791), said to have originated during the seating of the French National Assembly in 1789 in which the nobility took the seats on the President's right and left the Third Estate to sit on the left. Became general in U.S. and British political speech c. 1900.
Used since at least c. 1600 in various senses of "irregular, illicit;" earlier proverbial sense was "opposite of what is expressed" (mid-15c.). 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. To have two left feet "be clumsy" is attested by 1902. The Left Bank of Paris (left bank of the River Seine, as you face downstream) has been associated with intellectual and artistic culture since at least 1893.