Etymology
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toggle (n.)
1769, "pin passed through the eye of a rope, strap, or bolt to hold it in place," a nautical word of uncertain origin, perhaps a frequentative form of tog "tug." As a kind of wall fastener it is recorded from 1934. Toggle bolt is from 1794; toggle switch, the up-and-down sort, first attested 1938. In computing by 1979, in reference to a key which alternates the function between on and off when struck.
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Velcro (n.)

1958, proprietary name (Britain), from French vel(ours) cro(ché) "hooked velvet."

Here is a nonmetallic fastener with no mechanical parts. It is simply two strips of nylon, one woven with thousands of tiny protruding hooks, the other with loops. Pressed together, they catch like a burr to clothing, can't be parted except by peeling. American Velcro, Manchester, N.H., makes them to hold anything from pants to upholstery. [Popular Science, December 1958]
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clavicle (n.)

"collarbone," 1610s, from French clavicule "collarbone" (16c.), also "small key," from Medieval Latin clavicula "collarbone" (used c. 980 in a translation of Avicenna), special use of classical Latin clavicula, literally "small key, bolt," diminutive of clavis "key" (from PIE root *klau- "hook"); in the anatomical sense a loan-translation of Greek kleis "key, collarbone," which is from the same PIE source. So called supposedly from its function as the "fastener" of the shoulder. Related: Clavicular.

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Knickerbocker 
"descendant of Dutch settlers of New York," 1831, from Diedrich Knickerbocker, the name under which Washington Irving published his popular "History of New York" (1809). The pen-name was borrowed from Irving's friend Herman Knickerbocker, and literally means "toy marble-baker," from German knicker, schoolboy slang for "marble," apparently an agent-noun from the imitative verb knikken "to snap."
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snack (n.)
c. 1400, "a snatch or snap" (especially that of a dog), from snack (v.). Later "a snappish remark" (1550s); "a share, portion, part" (1680s; hence old expression go snacks "share, divide; have a share in"). Main modern meaning "a bite or morsel to eat hastily" is attested from 1757. Snack bar is attested from 1923. Commercial plural form snax attested from 1942 in the vending machine trade.
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tassel (n.)
c. 1300, "mantle fastener," from Old French tassel "tassel, fringe, hem; a fastening, clasp" (12c., Modern French tasseau), from Vulgar Latin *tassellus, said to be from Latin taxillus "small die or cube," a diminutive of talus "knucklebone (used as a die in gaming), ankle" (see talus (n.1)). But OED finds this doubtful and calls attention to the variant form tossel and suggests association with toss (v.). Meaning "hanging bunch of small cords" is first recorded late 14c.
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tack (n.1)
"clasp, hook, fastener," also "a nail" of some kind, c. 1400, from Old North French taque "nail, pin, peg" (Old French tache, 12c., "nail, spike, tack; pin brooch"), probably from a Germanic source (compare Middle Dutch tacke "twig, spike," Frisian tak "a tine, prong, twig, branch," Low German takk "tine, pointed thing," German Zacken "sharp point, tooth, prong"), from Proto-Germanic *tag-. Meaning "small, sharp nail with a flat head" is attested from mid-15c. The meaning "rope to hold the corner of a sail in place" is first recorded late 15c.
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ginger (n.)

mid-14c., from Old English gingifer, gingiber, from Late Latin gingiber, from Latin zingiberi, from Greek zingiberis, from Prakrit (Middle Indic) singabera, from Sanskrit srngaveram, from srngam "horn" + vera- "body," so called from the shape of its root. But this may be Sanskrit folk etymology, and the word may be from an ancient Dravidian word that also produced the Malayalam name for the spice, inchi-ver, from inchi "root."

The word apparently was readopted in Middle English from Old French gingibre (12c., Modern French gingembre). In reference to coloring, by 1785 of fighting cocks, 1885 of persons (gingery with reference to hair is from 1852). Meaning "spirit, spunk, temper" is from 1843, American English (see gin (v.1)). Ginger-ale is recorded by 1822, the term adopted by manufacturers to distinguish their product from ginger beer (1809), which was sometimes fermented. Ginger-snap as a type of hard cookie flavored with ginger is from 1855, American English.

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flirt (v.)
1550s, "to turn up one's nose, sneer at;" later "to rap or flick, as with the fingers" (1560s); "throw with a sudden movement," also "move in short, quick flights" (1580s). Perhaps imitative (compare flip (v.), also East Frisian flirt "a flick or light blow," flirtje "a giddy girl," which also might have fed into the English word), but perhaps rather from or influenced by flit (v.). Related: Flirted; flirting.

The main modern verbal sense of "play at courtship" (1777) probably developed from the noun (see flirt (n.)) but also could have grown naturally from the 16c. meaning "to flit inconstantly from object to object." To flirt a fan (1660s) was to snap it open or closed with a brisk jerk and was long considered part of the coquette's arsenal, which might have contributed to the sense shift. Or the word could have been influenced from French, where Old French fleureter meant "talk sweet nonsense," also "to touch a thing in passing," diminutive of fleur "flower" (n.) and metaphoric of bees skimming from flower to flower. French flirter "to flirt" is a 19c. borrowing from English.
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rat-race (n.)

also rat race, 1934 in reference to aviation training, from rat (n.) + race (n.1).

A rat race is ... a simple game of "follow the leader" in fighter planes. The leader does everything he can think of — Immelmanns, loops, snap rolls, and turns, always turns, tighter and tighter. [Popular Science, May 1941]

In the 1930s actual rat races of some sort are frequently mentioned among popular carnival and gambling attractions. Meaning "fiercely competitive struggle," especially to maintain one's position in work or life is by 1939. Rat-run is from 1870 in the sense of "maze-like passages by which rats move about their territory," but originally and usually in a derogatory transferred sense.

[Matthew] Milton was not, at the period we write of [c. 1811], at all in the ring ; for in the following March he was steward of a rat-race, held at a public-house in Shepherd's-market, where four of these "varmin," decorated with different coloured ribands, were started for a sweepstakes, round the clubroom, before a host of sportsmen. ["Sporting Incidents at Home and Abroad," The Sporting Review, May 1848]
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