Etymology
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Fibonacci (adj.)
1891 in reference to a series of numbers in which each is equal to the sum of the preceding two, from name of Leonardo Fibonacci (fl. c. 1200) Tuscan mathematician.
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Cartesian (adj.)
pertaining to the works or ideas of French philosopher and mathematician René Descartes (1596-1650), 1650s, from Cartesius, the Latinized form of his surname (regarded as Des Cartes) + -ian. In addition to his philosophy (based on the fundamental principle cogito, ergo sum), he developed a system of coordinates for determining the positions of points on a plane.
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Indian summer (n.)
"spell of warm, dry, hazy weather after the first frost" (happening anywhere from mid-September to nearly December, according to location), 1774, North American English (also used in eastern Canada), perhaps so called because it was first noted in regions then still inhabited by Indians, in the upper Mississippi valley west of the Appalachians, or because the Indians first described it to the Europeans. No evidence connects it with the color of fall leaves, or to a season of renewed Indian attacks on settlements due to renewed warm weather (a widespread explanation dating at least to the 1820s).

It is the American version of British All-Hallows summer, French été de la Saint-Martin (feast day Nov. 11), etc. Also colloquial was St. Luke's summer (or little summer), period of warm weather occurring about St. Luke's day (Oct. 18). An older and simpler name for it was autumn-spring (1630s).
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Fort Sumter 
military installation in South Carolina, U.S., begun in 1827, named for U.S. Revolutionary War officer and Congressman Thomas Sumter (1734-1832), "The Carolina Gamecock." The family name is attested from 1206, from Old French sommetier "driver of a pack horse" (see sumpter). The U.S. Civil War is held to have begun with the firing of rebel batteries on the government-held fort on April 12, 1861.
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Sumerian (adj.)
1874, from French Sumérien (1872), "pertaining to Sumer," name of a district in ancient Babylonia, once the seat of a great civilization. As the name of a language from 1887. Related: Sumeria.
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Peter 

masc. proper name, 12c., from Old English Petrus (genitive Pet(e)res, dative Pet(e)re), from Latin Petrus, from Greek Petros, literally "stone, rock" (see petrous), a translation of Syriac kefa "stone" (Latinized as Cephas), the nickname Jesus gave to apostle Simon Bar-Jona (Matthew xvi.17), historically known as St. Peter, and consequently a popular name among Christians (Italian Pietro, Spanish and Portuguese Pedro, Old French Pierres, French Pierre, etc.). As slang for "penis," attested from 1902, probably from identity of first syllable.

The common form of this very common name in medieval England was Peres (Anglo-French Piers), hence surnames Pierce, Pearson, etc. Among the diminutive forms were Parkin and Perkin.

To rob Peter to pay Paul (1510s, attested in slightly different wordings from late 14c.) might be a reference to the many churches dedicated to those two saints, and have sprung from the fairly common practice of building or enriching one church with the ruins or revenues of another. But the alliterative pairing of the two names is attested from c. 1400 with no obvious connection to the saints:

Sum medicyne is for peter þat is not good for poul, for þe diuersite of complexioun. [Lanfranc's "Chirurgia Magna," English translation, c. 1400]
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