Etymology
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rust (n.)

"red oxide of iron, red coating which forms on the surface of iron exposed to the air," Old English rust "rust," in late Old English also figurative, "anything tending to spiritual corrosion, a moral canker," related to rudu "redness," from Proto-Germanic *rusta- (source also of Frisian rust, Old High German and German rost, Middle Dutch ro(e)st), from PIE *reudh-s-to- (source also of Lithuanian rustas "brownish," rūdėti "to rust;" Latin robigo, Old Church Slavonic ruzda "rust"), from suffixed form of root *reudh- "red, ruddy."

As a morbid condition of plants caused by fungal growth, from mid-14c. U.S. colloquial rust-bucket for "old car or boat" is by 1945. Rust Belt "decayed urban industrial areas of mid-central U.S." (1984) was popularized in, if not coined by, Walter Mondale's presidential campaign.

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plant (n.)

Old English plante "young tree or shrub, herb newly planted, a shoot or strip recently sprouted from seed," from Latin planta "sprout, shoot, cutting" (source of Spanish planta, French plante), which is perhaps from an unattested verb *plantare "to drive in with the feet, push into the ground with the feet," or perhaps "to level the earth," from planta "sole of the foot," from nasalized form of PIE root *plat- "to spread."  German Pflanz, Irish cland, Welsh plant also are from Latin.

Broader sense of "any small vegetable life, vegetation generally" (sometimes popularly excluding trees), "an individual living being with material organization but not animal in nature" is recorded by 1550s.

Most extended usages are from the verb, on the notion of "something planted;" such as "construction for an industrial process," 1789, at first with reference to the machinery, tools, apparatus, etc., later also the building; also slang meaning "a spy" (1812). Many of these follow similar developments in the French form of the word.

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thread (n.)

Old English þræd "fine cord, especially when twisted" (related to þrawan "to twist"), from Proto-Germanic *thredu- "twisted yarn" (source also of Old Saxon thrad, Old Frisian thred, Middle Dutch draet, Dutch draad, Old High German drat, German Draht, Old Norse þraðr), literally "twisted," from suffixed form of PIE root *tere- (1) "to rub, turn." Meaning "spiral ridge of a screw" is from 1670s. Threads, slang for "clothes" is 1926, American English.

The silk line, as spun by the worm, is about the 5000th part of an inch thick; but a spider's line is perhaps six times finer, or only the 30,000th part of an inch in diameter, insomuch, that a single pound of this attenuated substance might be sufficient to encompass our globe. [John Leslie, "Elements of Natural Philosophy," Edinburgh, 1823]
Nuts and bolts you know as little things that put big things together. Actually, our whole industrial civilization hangs by a thread—a screw thread. [Popular Science, March 1949]
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develop (v.)
Origin and meaning of develop

1650s, "unroll, unfold" (a sense now obsolete), from French développer. It replaced earlier English disvelop (1590s, from French desveloper); both French words are from Old French desveloper, desvoleper, desvoloper "unwrap, unfurl, unveil; reveal the meaning of, explain," from des- "undo" (see dis-) + voloper "wrap up," which is of uncertain origin, possibly Celtic or Germanic.

The modern uses are figurative and emerged in English 18c. and after: Transitive meaning "unfold more fully, bring out the potential in" is by 1750; intransitive sense of "come gradually into existence or operation" is by 1793; that of "advance from one stage to another toward a finished state" is by 1843. The intransitive meaning "become known, come to light" is by 1864, American English.

The photographic sense "induce the chemical changes necessary to cause a latent picture or image to become visible" is from 1845; the real estate sense of "convert land to practical or profitable use" is by 1865. Related: Developed; developing.Developing as an adjective in reference to poor or primitive countries or nations that are advancing in economic, industrial, and social conditions is by 1960.

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mill (n.1)

Middle English mille, "building fitted to grind grain," Old English mylen "a mill" (10c.), an early Germanic borrowing from Late Latin molina, molinum "mill" (source of French moulin, Spanish molino), originally fem. and neuter of molinus "pertaining to a mill," from Latin mola "mill, millstone," related to molere "to grind," from PIE root *mele- "to crush, grind." The -n- gradually was lost in English but survives in the surname Milner. Also from Late Latin molina, directly or indirectly, are German Mühle, Old Saxon mulin, Old Norse mylna, Danish mølle, Old Church Slavonic mulinu.

The meaning "mechanical device for grinding grain for food" is from 1550s. The broader sense of "machine for grinding or pulverizing any solid substance" is attested from 1670s. Other types of manufacturing machines driven by wind or water, that transform raw material by a process other than grinding began to be called mills by early 15c. Sense of "large building fitted with industrial machinery for manufacturing" is from c. 1500. In old slang also "a typewriter" (1913); "a boxing match or other pugilistic bout" (1819).

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hammer (n.)

Old English hamor "hammer," from Proto-Germanic *hamaraz (source also of Old Saxon hamur, Middle Dutch, Dutch hamer, Old High German hamar, German Hammer). The Old Norse cognate hamarr meant "stone, crag" (it's common in English place names), and suggests an original sense of the Germanic words as "tool with a stone head," which would describe the first hammers. The Germanic words thus could be from a PIE *ka-mer-, with reversal of initial sounds, from PIE *akmen "stone, sharp stone used as a tool" (source also of Old Church Slavonic kamy, Russian kameni "stone"), from root *ak- "be sharp, rise (out) to a point, pierce."

As a part of a firearm, 1580s; as a part of a piano, 1774; as a small bone of the ear, 1610s. Figurative use of "aggressive and destructive foe" is late 14c., from similar use of French martel, Latin malleus. To go at it hammer and tongs "with great violence and vigor" (1708) is an image from blacksmithing (the tongs hold the metal and the hammer beats it). Hammer and sickle as an emblem of Soviet communism attested from 1921, symbolizing industrial and agricultural labor.

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cotton-picking (adj.)

as a deprecatory term first recorded in a Bugs Bunny cartoon, but a similar noun cotton-picker meaning "contemptible person" dates to around 1919, perhaps with racist overtones that have faded over the years. Before mechanization, cotton picking was the most difficult labor on a plantation.

I drove out to a number of the farms near Denison and found many very young white children working all day in the hot sun picking and dragging sacks of cotton. In one field the labor corps consisted of one woman and six children, one of them 5 years, one 6 years, one 7 years, one 9 years, and two about 11. The father was plowing. The 5 and 6 year olds worked all day as did the rest. The 7-year-old said he picked 50 pounds a day and the 9 year old 75 pounds. (A good picker averages several hundred a day.) School begins late on account of the cotton picking, but the children nearly all prefer school to the picking. Picking hours are long, hot, and deadly monotonous. While the very young children seem to enjoy it, very soon their distaste for it grows into all-absorbing hatred for all work. ["Field Notes of Lewis W. Hine, Child-Labor Conditions in Texas," report to U.S. Congressional Commission on Industrial Relations, 1916]
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