pentagon (n.)

1560s, "plane figure with five angles and five sides," from French pentagone (13c.) or directly from Late Latin pentagonum "pentagon," from Greek pentagōnon, a noun use of the neuter of the adjective pentagōnos "five-angled," from pente "five" (from PIE root *penkwe- "five") + gōnia "angle, corner" (from PIE root *genu- (1) "knee; angle"). The U.S. military headquarters known as the Pentagon was completed in 1942, and so called for its shape; used allusively for "U.S. military leadership" from 1945; Pentagonese "U.S. official military jargon" is by 1951. Related: Pentagonal.

In nature, pentagonal symmetry is rare in inanimate forms. Packed soap bubbles seem to strive for it but never quite succeed, and there are no mineral crystals with true pentagonal structures. But pentagonal geometry is basic to many living things, from roses and forget-me-nots to sea urchins and starfish. [Robert Bringhurst, "The Elements of Typographic Style," 1992]
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normalcy (n.)

1857, "mathematical condition of being at right angles, state or fact of being normal in geometry," from normal + -cy. The word has been associated since 1920 with U.S. president Warren G. Harding (who campaigned that year under the slogan "Return to Normalcy," meaning pre-World War I conditions). Previously normalcy was used mostly in the mathematical sense and the word preferred by purists for "a normal situation" is normality. Harding's use of it was derided during his administration as an example of his much-belittled incompetence with the language (Democratic politician William G. McAdoo Jr. called Harding’s speeches "an army of pompous phrases moving across the landscape in search of an idea"). 

America’s present need is not heroics, but healing; not nostrums, but normalcy; not revolution, but restoration; not agitation, but adjustment; not surgery, but serenity; not the dramatic, but the dispassionate; not experiment, but equipoise; not submergence in internationality, but sustainment in triumphant nationality. [Harding, "Readjustment" speech, May 24, 1920]
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ellipsis (n.)

1560s, "an ellipse" in geometry, from Latin ellipsis, from Greek elleipsis "a falling short, defect, ellipse in grammar," noun of action from elleipein "to fall short, leave out," from en- "in" (see en- (1)) + leipein "to leave" (from PIE root *leikw- "to leave").

Grammatical and rhetorical sense in English first recorded 1610s: "a figure of syntax in which a part of a sentence or phrase is used for the whole, by the omission of one or more words, leaving the full form to be understood or completed by the reader or hearer."

In printing, "a mark or marks denoting the omission of letters, words, or sentences," by 1867. Dashes, asterisks, and period have been used to indicate it. In reading aloud, a short pause was proper at a grammatical ellipsis in the writing.

WHEN a word or words are omitted by the figure ellipsis, a pause is necessary where the ellipsis occurs. [Robert James Ball, "The Academic Cicero; or Exercises in Modern Oratory," Dublin, 1823] 

Probably the association of the typographical symbol with a pause in speaking is why 20c. writers began to use the three periods to denote a pause or an interruption in dialogue, creating a potential confusion noted by 1939. Related: Ellipticity.

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