shoestring (n.)

Middle English sho, "low-cut covering for the human foot," from Old English scoh, from Proto-Germanic *skokhaz (source also of Old Norse skor, Danish and Swedish sko, Old Frisian skoch, Old Saxon skoh, Middle Dutch scoe, Dutch schoen, Old High German scuoh, German Schuh, Gothic skoh). No known cognates outside Germanic, unless it somehow is connected with PIE root *skeu- "cover" (source also of second element in Latin ob-scurus).

The old plural form shoon lasted until 16c. The meaning "metal plate or rim nailed to the hoof of a horse or beast of burden to protect it from injury" is attested from c.1300. The distinction between shoe and boot (n.) is attested from c. 1400.

To stand in someone's shoes "see things from his or her point of view" is attested from 1767. Old shoe as a type of something worthless is attested from late 14c.

Shoes tied to the fender of a newlywed couple's car preserves the old custom (mentioned from 1540s) of throwing an old shoe at or after someone to wish them luck. Perhaps the association is with dirtiness, on the "muck is luck" principle.

Middle English streng, from Old English streng "line, slender cord, thick thread," also a rope, also the string of a bow or harp, which tightly stretched produces the tone; in plural "tackle, rigging;" also "lineage, race." This is from Proto-Germanic *strangiz (source also of Old Norse strengr, Danish streng, Middle Dutch strenge, Dutch streng, Old High German strang, German Strang "rope, cord"). This is reconstructed to be from *strang- "taut, stiff," from a PIE root *strenk- "tight, narrow."

The sense gradually restricted by early Middle English to lines that are smaller than a rope. The meaning "a number of objects arranged in a file or on a string" is recorded by late 15c.; of successes, disasters, etc., "continuous series or succession," by 1710.

The Old English meaning "ligaments, tendons" is preserved in hamstring (n.), heart-strings.

To pull strings "control the course of affairs" (1860) is an image from marionette theater.

The meaning "limitation, stipulation" (1888) is American English, in political jargon, and could be from the (then-)common April Fool's prank of setting down a money-purse as though dropped, then from seclusion tugging it away with a hidden string when someone stoops to pick it up. Hence the figurative phrase no strings attached (by 1951), though this is confusable with the notion of puppet strings.

First string, second string, etc. in athletics (1863) is said to be from archers carrying a spare bowstring in the event the other broke. The figure of have two strings to one's bow "have alternative resources" is in English by 1540s.

Strings "stringed instruments" is attested from mid-14c.; string-band "band composed of stringed instruments" is by 1889, American English. String bean is from 1759, probably so called for its fibrous threads; string bikini is by 1974, for the straps that hold the fabric together.