Re: Latin opacus / opa:cus/

--- In cybalist@yahoogroups.com, "Joao S. Lopes" <josimo70@...> wrote:

>
> Any plausible etymology for Latin opa:cus, "opaque, shady"
>
> JS Lopes
>

A possible connection?

Ernout-Meillet:

'opācus, -a, -um: -a uocantur umbrosa; Fest.200,5; "qui est à l'ombre" (opposé à aprīcus, cf. Cic. Part. Or. 10 fin, Varr., R.R.3, 14, 2); et par suite "obscur, où la lumière ne pénètre pas".
- Ancien (Pacuv.), usuel, classique.
A la différence de obscūrus ne s'emploie pas au sens figuré.
M.L.6069.
Dérivés et composés:
opācitās (époq.imp.);
opācō,-ās: ombrager; M.L.6068, et
inopācō (Col.);
inopācus = `άσκιoς (Gloss.).

On admet souvent qu'il y a ici un dérivé de la préposition op-, ob- avec un suffixe *-āko-. Mais pareil suffixe n'est guère usuel en latin; du reste il ne s'ajoute pas à des prépositions (le type de skr. apāka- est tout différent; v. sous oculus). Et cette étymologie ne rendrait, en tout cas, pas compte du sens matériel de opācus. Donc étymologie inconnue.

opalus, -Ä« m.: opale (Plin., Isid. ).
Sans doute mot d'emprunt; le gr. a `οπάλλιος, qui semble provenir du skr. úpalah. "pierre".'


http://en.wikipedia.org/wiki/Opal
'Opal's internal structure makes it diffract light; depending on the conditions in which it formed it can take on many colors. Opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semi-transparent. For gemstone use, its natural color is often enhanced by placing thin layers of opal on a darker underlying stone, like basalt.'
...
'Precious opal shows a variable interplay of internal colors and even though it is a mineraloid, it does have an internal structure. At micro scales precious opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic close-packed lattice. These ordered silica spheres produce the internal colors by causing the interference and diffraction of light passing through the microstructure of the opal.[5] It is the regularity of the sizes and the packing of these spheres that determines the quality of precious opal. Where the distance between the regularly packed planes of spheres is approximately half the wavelength of a component of visible light, the light of that wavelength may be subject to diffraction from the grating created by the stacked planes. The spacing between the planes and the orientation of planes with respect to the incident light determines the colors observed. The process can be described by Bragg's Law of diffraction.
Visible light of diffracted wavelengths cannot pass through large thicknesses of the opal. This is the basis of the optical band gap in a photonic crystal, of which opal is the best known natural example. In addition, microfractures may be filled with secondary silica and form thin lamellae inside the opal during solidification. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, which is correctly termed play of color. Contrarily, opalescence is correctly applied to the milky, turbid appearance of common or potch opal. Potch does not show a play of color.
The veins of opal displaying the play of color are often quite thin, and this has given rise to unusual methods of preparing the stone as a gem. An opal doublet is a thin layer of opal, backed by a swart mineral such as ironstone, basalt, or obsidian. The darker backing emphasizes the play of color, and results in a more attractive display than a lighter potch.'

So perhaps originally opācus = "opal-like", later generalized to "opaque"? Just a thought.


Torsten