Etymology
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neurasthenia (n.)
"nervous exhaustion," 1854, medical Latin, from neur- (form of neuro- before a vowel) + asthenia "weakness" (see asthenia). Related: Neurasthenic.
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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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Ruy Lopez (n.)
type of chess opening, 1876, from Ruy López de Segura (fl. 1560), Spanish bishop and writer on chess, who developed it.
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floruit 
"period during which a historical person's life work was done," 1843, Latin, literally "he flourished," third person singular perfect indicative of florere "to flourish, to bloom" (see flourish (v.)). Usually in abbreviation fl. The third person singular present subjunctive of the verb, floreat, sometimes is attached to proper names "to indicate the hope that the named person, institution, etc., may prosper" [OED].
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flounder (v.)
"struggle awkwardly and impotently," especially when hampered somehow, 1590s, of uncertain origin, perhaps from an alteration of founder (n.), influenced by Dutch flodderen "to flop about," or native verbs in fl- expressing clumsy motion. Figurative use is from 1680s. Related: Floundered; floundering. As a noun, "act of struggling," by 1867.
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neuro- 

before vowels neur-, word-forming element meaning "pertaining to a nerve or nerves or the nervous system," from Greek neura "nerve" (Galen), originally "sinew, bowstring," also neuron "sinew, string (of a bow or musical instrument); cord; penis;" in plural "strength, vigor," from PIE *(s)neuro- "tendon, sinew" (see nerve (n.)). In Greek, puppets were neurospastos, literally "drawn by strings."

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Teflon (n.)
commercially important synthetic polymer, 1945, proprietary name registered in U.S. by du Pont, from chemical name (poly)te(tra)fl(uoroethylene) + arbitrary ending -on; popularized as a coating of non-stick pans in 1960s; metaphoric extension, especially in reference to U.S. President Ronald Reagan, is attested from an Aug. 2, 1983, speech on the floor of Congress by Pat Schroeder.
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spinet (n.)

1660s, spinette, "small harpsichord," from French espinette (16c., Modern French épinette), from Italian spinetta, said by Scaliger to be a diminutive of spina "thorn, spine," from Latin spina "thorn" (see spine), so called because the strings were plucked with thorn-like quills [Barnhart]. The other theory (favored by Klein and assigned "greater probability" by OED) dates to early 17c. and claims the word is from the name of the Venetian inventor, Giovanni Spinetti (fl. c. 1503). As "small, upright piano" from 1936.

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flank (n.)
late Old English flanc "flank, fleshy part of the side," from Old French flanc "hip, side," from Frankish or another Germanic source, from Proto-Germanic *hlanca- (source also of Old High German (h)lanca, Middle High German lanke "hip joint," German lenken "to bend, turn aside;" Old English hlanc "loose and empty, slender, flaccid;" Old Norse hlykkr "a bend, noose, loop"), from PIE root *kleng- "to bend, turn" (see link (n.)). Showing characteristic change of Germanic hl- to Romanic fl-. The military sense is first attested 1540s. Meaning "side" of anything is by 1620s. As an adjective, "pertaining to the flank or side," 1660s. Related: Flanked; flanking.
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flirt (n.)
1540s, "joke, jest, stroke of wit, contemptuous remark," from flirt (v.). By 1560s as "a pert young hussey" [Johnson], and Shakespeare has flirt-gill (i.e. Jill) "a woman of light or loose behavior" (Fletcher formalizes it as flirt-gillian), while flirtgig was a 17c. Yorkshire dialect word for "a giddy, flighty girl." One of the many fl- words suggesting loose, flapping motion and connecting the notions of flightiness and licentiousness. Compare English dialect and Scottish flisk "to fly about nimbly, skip, caper" (1590s); source of Scott's fliskmahoy "girl giddy and full of herself." The meaning "person who plays at courtship" is from 1732 (as the name of female characters in plays at least since 1689 (Aphra Behn's "The Widow Ranter")). Also in early use sometimes "person one flirts with," though by 1862 this was being called a flirtee.
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