Etymology
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cold feet (n.)

1893, American English, in the figurative sense "fear or doubt that reverses an intention to do something;" the presumed Italian original (avegh minga frecc i pee) is a Lombard proverb meaning "to have no money," but some of the earliest English usages refer to gamblers, so a connection is possible.

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leap year (n.)
"year containing 366 days," late 14c., lepe gere (not in Old English), from leap (v.) + year. Probably so called from its causing fixed festival days, which normally advance one weekday per year, to "leap" ahead one day in the week. Compare Medieval Latin saltus lunae (Old English monan hlyp) "omission of one day in the lunar calendar every 19 years."

Dutch schrikkeljaar "leap year" is from Middle Dutch schricken "leap forward," literally "be startled, be in fear." The 29th of February is schrikkeldag. Danish skudaar, Swedish skottår are literally "shoot-year;" German schaltjahr is from schalten "insert, intercalate." The Late Latin phrase was annus bissextilis, source of the Romanic words; compare bissextile.
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world war (n.)

attested by 1898 as a speculation.

If through fear of entangling alliances the United States should return the Philippines to Spain, Mr. Page asserted that the predatory nations would swoop down upon them and a world war would result. [New York Times, Dec. 16, 1898]

Applied to the first one almost as soon as it began in 1914 ("England has Thrown Lot with France in World War" — headline, Pittsburgh Press, Aug. 2, 1914). World War I was coined 1939, replacing Great War as the most common name for it; First World War, World War II, and Second World War all also are from 1939. Old English had woruldgewinn, woruldgefeoht, both of which might be translated "world war," but with "world" in the sense of "earthly, secular."

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