Etymology
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forty (adj., n.)

"1 more than thirty-nine, twice twenty; the number which is one more than thirty-nine; a symbol representing this number;" early 12c., feowerti, from Old English feowertig, Northumbrian feuortig "forty," from feower "four" (from PIE root *kwetwer- "four") + tig "group of ten" (see -ty (1)). Compare Old Saxon fiwartig, Old Frisian fiuwertich, Dutch veertig, Old High German fiorzug, German vierzig, Old Norse fjorir tigir, Gothic fidwor tigjus.

[T]he number 40 must have been used very frequently by Mesha's scribe as a round number. It is probably often used in that way in the Bible where it is remarkably frequent, esp. in reference to periods of days or years. ... How it came to be so used is not quite certain, but it may have originated, partly at any rate, in the idea that 40 years constituted a generation or the period at the end of which a man attains maturity, an idea common, it would seem, to the Greeks, the Israelites, and the Arabs. ["The International Standard Bible Encyclopedia," James Orr, ed., Chicago, 1915]

Forty winks "short sleep" is attested from 1821; in early use associated with, and perhaps coined by, English eccentric and lifestyle reformer William Kitchiner M.D. (1775-1827). Forty-niner in U.S. history was an adventurer to California (usually from one of the eastern states) in search of fortune during the gold rush of 1849.

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quarantine (n.)

1660s, "period a ship suspected of carrying contagious disease is kept in isolation," from Italian quaranta giorni, literally "space of forty days," from quaranta "forty," from Latin quadraginta"forty" (related to quattuor "four," from PIE root *kwetwer- "four").

The name is from the Venetian policy (first enforced in 1377) of keeping ships from plague-stricken countries waiting off its port for 40 days to assure that no latent cases were aboard. Also see lazaretto. The extended sense of "any period of forced isolation" is from 1670s.

Earlier in English the word meant "period of 40 days in which a widow has the right to remain in her dead husband's house" (1520s), and, as quarentyne (15c.), "desert in which Christ fasted for 40 days," from Latin quadraginta "forty."

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fortieth (adj., n.)

"next in order after the thirty-ninth; an ordinal numeral; being one of forty equal parts into which a whole is regarded as divided;" c. 1200, fowertiþe, from Old English feowertigoða, from feowertig (see forty) + -th (1). Compare Old Norse fertugonde, Swedish fyrationde, Danish fyrretyvende.

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Quadragesima (n.)

"Lent," c. 1600, from Medieval Latin quadragesima (dies) "the fortieth (day)," altered diminutive of Latin quadrigesimus "fortieth," from quadriginta "forty," related to quattuor "four" (from PIE root *kwetwer- "four"). So called because it lasts forty days. Earlier in English in nativized form Quadragesime (mid-15c.). Related: Quadragesimal. Via the Vulgar Latin form *quaragesima come Old French quaresme, Modern French carême, Spanish cuaresma, Italian quaresima, also ultimately Irish carghas, Gaelic carghus, Welsh garaways.

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fifty (adj., n.)

"1 more than forty-nine, twice twenty-five; the number which is one more than forty-nine; a symbol representing this number;" Old English fiftig "fifty; a set of fifty," from fif "five" (from PIE root *penkwe- "five") + -tig "group of ten" (see -ty (1)). Compare Old Frisian fiftich, Old Norse fimm tigir, Dutch vijftig, Old High German fimfzug, German fünfzig, Gothic fimf tigjus. U.S. colloquial fifty-fifty "in an even division" is from 1908.

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hairbreadth (n.)

also hairsbreadth, hairs-breadth, hair's breadth, from late 15c. as a measure of minute exactness. It is said to once have been a formal unit of measure equal to one-forty-eighth of an inch. From hair + breadth.

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eighty (adj., n.)

"1 more than seventy-nine, twice forty; the number which is one more than seventy-nine; a symbol representing this number;" late 13c., eigteti, from eight + -ty (1). Replacing Old English hundeahtatig, with hund- "ten." Related: Eightieth.

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fiftieth (adj., n.)

"next in order after the forty-ninth; an ordinal numeral; being one of fifty equal parts into which a whole is regarded as divided;" Old English fifteogoða "fiftieth;" see fifty + -th (1). Compare Old Norse fimmtugande, and, with a different suffix, Old Frisian fiftichsta, Dutch vijftigste, Old High German fimfzugsto, German fünfzigste.

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lower (adj.)

Middle English lawar, lower, lougher, earlier lahre (c. 1200), comparative of lah "low" (see low (adj.)). As an adverb from 1540s. Lower-class is from 1772. Lower 48, "the forty-eight contiguous states of the United States of America, excluding Alaska and Hawaii," is by 1961 in an Alaska context (Hawaii actually is "lower" on the globe than all of them).

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cyan- 

word-forming element used in science for the carbon-nitrogen compound radical, from a Latinized form of Greek kyanos "dark blue" (see cyan).

The immediate source of its use in science is French cyanogène, the name given to the compound radical by Gay-Lussac. He called it that because it first had been obtained by heating the dye pigment powder known as Prussian blue (see Prussian).

The cyanogen radical was one of the first examples of a 'compound radical' and was of importance in the development of structural chemistry during the next forty years. [Flood, "Origins of Chemical Names"]  
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