slink (v.)

c. 1300, "hand-held implement for throwing stones" (consisting of a strap and two strings), from an unidentified continental Germanic source (such as Middle Low German slinge "a sling") from verbs meaning "swing to and fro, wind, twist" (see sling (v.1)).

The notion probably is of being twisted and twirled before it is released. The piece of stone or metal hurled from it is a sling-stone (late 14c.). The older English word for this ancient weapon was lithere (Old English liþere, related to leather).

Some of the sense developments might have been influenced by Low German cognates. The sense of "loop for lifting or carrying heavy objects" is recorded by early 14c. As "leather shoulder strap for a rifle, etc.," by 1711. The meaning "piece of cloth tied in a hanging loop around the neck to support an injured arm" is attested by 1720. A Middle English medical word for "sling or supporting loop used in treating dislocations" was stremb (early 15c., Chauliac, who also has suspensorie), from Medieval Latin stremba. 

The Greeks, Romans, and Carthaginians had bodies of slingers attached to their armies, recruited especially from the inhabitants of the Balearic Isles. The use of the sling continued among European armies to the sixteenth century, at which time it was employed to hurl grenades. [Century Dictionary]

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).