Etymology
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valve (n.)
late 14c., "one of the halves of a folding door," from Latin valva (plural valvae) "section of a folding or revolving door," literally "that which turns," related to volvere "to roll," from PIE root *wel- (3) "to turn, revolve." Sense extended 1610s to "membranous fold regulating flow of bodily fluids;" 1650s to "mechanical device that works like an anatomical valve;" and 1660s in zoology to "halves of a hinged shell." Related: Valved.
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univalve 
of mollusks and shells, 1660s (noun and adjective), from uni- + valve.
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bivalve (adj.)
1660s in reference to mollusks with hinged double shells; 1670s in reference to shutters or doors having two folding parts; from bi- + valve. The noun is 1680s in the mollusk sense.
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*wel- (3)
Proto-Indo-European root meaning "to turn, revolve," with derivatives referring to curved, enclosing objects.

It forms all or part of: archivolt; circumvolve; convoluted; convolution; devolve; elytra; evolution; evolve; Helicon; helicopter; helix; helminth; lorimer; ileus; involve; revolt; revolution; revolve; valve; vault (v.1) "jump or leap over;" vault (n.1) "arched roof or ceiling;" volte-face; voluble; volume; voluminous; volute; volvox; volvulus; vulva; wale; walk; wallet; wallow; waltz; well (v.) "to spring, rise, gush;" welter; whelk; willow.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit valate "turns round," ulvam "womb, vulva;" Lithuanian valtis "twine, net," vilnis "wave," apvalus "round;" Old Church Slavonic valiti "roll, welter," vlŭna "wave;" Greek eluein "to roll round, wind, enwrap," eilein "twist, turn, squeeze; revolve, rotate," helix "spiral object;" Latin volvere "to turn, twist;" Gothic walwjan "to roll;" Old English wealwian "roll," weoloc "whelk, spiral-shelled mollusk;" Old High German walzan "to roll, waltz;" Old Irish fulumain "rolling;" Welsh olwyn "wheel."
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mitral (adj.)

c. 1600, "resembling a mitre, of or pertaining to a mitre," from French mitral, from Modern Latin mitralis, from Latin mitra (see mitre). The mitral valve of the heart is so called from 1705, from Modern Latin mitrales valvulae.

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choke (n.)

1560s, "quinsy," from choke (v.). Meaning "action of choking" is from 1839. Meaning "valve which controls air to a carburetor" first recorded 1926; earlier it meant "constriction in the bore of a gun" (1875).

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reflux (n.)

early 15c., "a flowing back" (of the sea, etc.), "ebb tide," also figurative of instability, from Medieval Latin refluxus, from Latin re- "back, again" (see re-) + fluxus "a flowing," from fluere "to flow" (see fluent). Digestive sense is recorded from 1937; reflux-valve is attested by 1853.

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throttle (n.)
1540s, "throat;" it appears to be an independent formation from throat, perhaps a diminutive form, not derived directly from the verb. The mechanical sense is first recorded 1872, short for throttle-valve (1824). Full-throttle (allowing maximum speed) is from 1848 in reference to steam engines.
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bypass (n.)
also by-pass, 1848, "small pipe passing around a valve in a gasworks" (for a pilot light, etc.), from the verbal phrase; see by + pass (v.). First used 1922 for "road for the relief of congestion;" figurative sense is from 1928. The heart operation was first so called 1957.
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spigot (n.)
late 14c., "plug used to stop the hole of a cask," according to Barnhart probably from Old French *espigot (compare Gascony dialect espigot "core of a fruit, small ear of grain"), diminutive of Old Provençal espiga "ear of grain," from Latin spica "ear of grain" (see spike (n.2)). Meaning "valve for controlling the flow of a liquid" is from 1520s; the connecting notion is "that which controls or restrains."
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