As we move along the paths of technology and human invention, our skill sets and our language change along with our manner of life. But because so much of language, especially idiom, is built upon metaphor, as we lose understanding of past ways of living, those metaphors die, and become complicated literary allusions.
Take, for instance “dyed-on-the-wool,” which Ngaio Marsh used in a punning title of her mystery novel, Died in the Wool. The idiom really is “dyed,” and dyed-in-the-wool means, according to the AHD, “Thoroughgoing; out-and-out: a dyed-in-the-wool populist.” You usually see the idiom used in a political context, as in “Kennedy was a dyed in the wool Democrat.” SyedDin-the-wool can be used for other fields as well; I’m a dyed-in-the-wool Macintosh fan. The idiom derives from the practice of dying wool that has been washed, combed or “carded” to remove tangles and bits of trash, but which has not ye been spun into yarn. Wool dyed in after being washed and carded but before it is spun tends to be more thoroughly and permanently colored than wool dyed after it is spun.
In an historical, etymological context, the first recorded use of dyed in the wool as a metaphor (according to the OED) was by Richard Hooker in 1597. In Laws of Ecclesiastical Polity Hooker commented that
Children as it were in the Wooll of their infancie died with hardnesse may neuer afterwards change colour” (V. lxxii. S18).
Dyed in the wool is very much a metaphor in Hooker’s use, a sheepish metaphor to express the idea that if people are raised from childhood accustomed to austerity and temperance, then the virtues of austerity and temperance will be part of them, as if dyed in the wool. Oddly, as the OED notes, dyed-in-the-wool is now much more common in American English than in British English, though the phrase should usually be hyphenated.
The similarly sheepish idiom of a bellwether day in reference to stocks; that’ an idiom derived from the wether, or castrated ram, who leads the flock and wears a bell around his neck. The AHD defines a bellwether as “One that serves as a leader or as a leading indicator of future trends.”This too is an idiom we inherited from Britain, but there, oddly, a “bell weather day” is a bad day; bellwether seems to refer to a negative or downward trend. The OED offers, in addition to the traditional sheep-with-bell definition, the following “a leader; contemptuously: the ring-leader, the worst of the lot.’In standard American use, while bellwether refers to a leader or leading trend, the phrase is neutral. Sheep will follow a bellwether over a cliff, or into a canyon, no matter how foolish the action, so the idiom is not without natural cause. Indeed, we still use the phrase “like lambs to the slaughter, ” to refer to someone who unquestioningly follows others, no matter how life threatening and dangerous their action may be.
There are other sheepish idioms preserved as metaphoric fossils in English. We might also think of the phrase black sheep to refer to a sheep with black or dark wool, but black sheep also can mean “One who is considered disreputable or disgraceful by his or her relatives or associates.” We count sheep, a thankless, difficult and often boring task when we wish to fall asleep. We refer to someone who is reticent, even shy, as sheepish. We also use sheepish to refer to someone who has been “Embarrassed, as by consciousness of a fault,” often in the phrase “sheepish grin.”