Etymology
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ground floor (n.)
also ground-floor, c. 1600, from ground (n.) + floor (n.); figurative use is from 1864.
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ground zero (n.)
1946, originally with reference to atomic blasts. In reference to the Sept. 11, 2001, terrorist attack on New York, it was in use by Sept. 13.
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pied a terre (n.)
"small town house or rooms used for short residences," 1829, French, pied à terre, literally "foot on the ground."
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gefilte fish (n.)
1892, gefüllte Fisch, not a species but a loaf made from various kinds of ground fish and other ingredients; the first word is Yiddish, from German gefüllte "stuffed," from füllen "to fill" (from PIE root *pele- (1) "to fill").
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color-blindness (n.)

also colour-blindness, "incapacity for perceiving certain colors due to an absence or weakness of the sensation upon which the power of distinguishing them depends," 1844, the native word, used in England instead of French daltonisme (by 1828), after English chemist John Dalton (1766-1844), who published a description of it in 1794. From color (n.) + blindness.

The continental philosophers have named it Daltonism, a name which has been strongly objected to by almost every English writer who has discussed the subject, on the ground of the inexpediency and undesirableness of immortalizing the imperfections or personal peculiarities of celebrated men by title of this kind. ... The name "Color-Blindness," proposed by Sir D. Brewster, seems in every respect unexceptionable. [Littell's Living Age, vol. v, April 1845]

Noted as inexact (very few people who can see are blind to all color), "the term is applied with much laxity to any constitutional inability to discriminate between colours" [OED]. In figurative use, with reference to race or ethnicity, it is attested from 1866, American English. Related: color-blind (adj.), which is attested from 1854.

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lucus a non lucendo 

a phrase that stands for "absurd etymology," or generally "anything illogical, outrageous hypothesis," 1711, from the Latin phrase, taken as the outstanding example of such an error.

"A grove (lucus) [is so called] from not (a non) being light" (lucendo, ablative of lucere "to shine;" see light (n.)). That is, it is called a grove because light doesn't get into it. This explanation is found in a commentary on Virgil (Aeneid 1.22) by Servius, a 4th century grammarian, among other places. Other ancient grammarians (notably Quintilian) found it paradoxical and absurd, based on nothing more than the similarity in sound between the two words.

Modern scholarship, however, concludes that lucus and lucere probably do come both from the same PIE root (*leuk-) meaning "light, bright." De Vaan writes: "Lucus 'sacred grove, wood,' from PIE *louk-o- 'light place,' with cognates in Sanskrit loka- 'free space, world,' Lithuanian laukas 'field, land,' Latvian lauks 'field, clearing in the woods,' Old High German loh 'clearing' and English lea 'open field, meadow, piece of untilled grassy ground.' " Apparently the primeval notion in *louk-o- was a lighter place in a thick forest. Migration, change of climate, or felling of the woods might have shifted the meaning.

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