Etymology
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plot (n.)

late Old English plot "small piece of ground of defined shape," a word of unknown origin. The sense of "ground plan," and thus "map, chart, survey of a field, farm, etc." is from 1550s. Plat is a Middle English collateral form. The meaning "a secret, plan, fully formulated scheme" (usually to accomplish some evil purpose) is from 1580s, probably by accidental similarity to complot, from Old French complot "combined plan" (compare the sense evolution of plan), itself a word of unknown origin, perhaps a back-formation from compeloter "to roll into a ball," from pelote "ball." OED says "The usage probably became widely known in connexion with the 'Gunpowder Plot.' "

The meaning "set of events in a story, play, novel, etc." is from 1640s. Plot-line (n.) "main features of a story" is attested by 1940; earlier, in theater, "a sentence containing matter essential to the comprehension of the play's story" (1907).

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plot (v.)

1580s, "to make a map or diagram of, lay down on paper according to scale;" also "to lay plans for, conspire to effect or bring about" (usually with evil intent), from plot (n.). Intransitive sense of "to form a plan or device" is from c. 1600. Related: Plotted; plotter; plotting.

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subplot (n.)
also sub-plot, 1812 in literature, from sub- + plot (n.).
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marplot (n.)

"one who by officious interference defeats a design," 1708, the name of a character in Susanna Centlivre's comedy "The busie body;" from mar (v.) + plot (n.).

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plat (n.)

"flat piece of ground," mid-15c. (mid-13c. in surnames), a variant of plot (n.) assimilated to Middle English plat (adj.) "flat," which is from Old French plat "flat, stretched out" (see plateau (n.)). See OED plat sb.3 for full explanation.

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denouement (n.)

"the solution of a mystery, the winding up of a plot, the outcome of a course of conduct," 1752, from French dénouement "an untying" (of plot), from dénouer "untie" (Old French desnouer) from des- "un-, out" (see dis-) + nouer "to tie, knot," from Latin nodus "a knot," from PIE root *ned- "to bind, tie."

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machinate (v.)

c. 1600, "to lay plots, intrigue," a back-formation from machination, or else from Latin machinatus, past participle of machinari "to contrive skillfully; to design, scheme, plot." Transitive sense of "to plan, contrive, form (a plot, scheme, etc.)" also is from c. 1600. Related: Machinated; machinating; machinator.

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backyard (n.)
also back-yard, "plot of ground at the rear of a house," 1650s (perhaps early 15c.), from back (adj.) + yard (n.1).
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machination (n.)

late 15c., machinacion, "a plotting, an intrigue," from Old French machinacion "plot, conspiracy, scheming, intrigue" and directly from Latin machinationem (nominative machinatio) "device, contrivance, machination," noun of action from past-participle stem of machinari "to contrive skillfully, to design; to scheme, to plot," from machina "machine, engine; device trick" (see machine (n.)). Related: Machinations.

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intrigue (n.)
1640s, "a clandestine plot;" 1660s, "secret plotting," probably from intrigue (v.). Also used from 1660s as "clandestine or illicit sexual encounter."
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