PLOT, a term originally meaning a space of ground used for a specific purpose, especially as a building site, formerly in frequent usage in the sense of a plan, a surveyed space of ground; hence the literary sense of a plan or design. The word is of doubtful origin; there is a collateral form " plat," which appears in the 16th century, according to the New English Dictionary, under the influence of " plat, " flat place, surface (Fr. plat, Late Lat. plallus, probably from Gr. TrXorus, broad). Skeat (Etym. Diet.) refers " plot," in the sense of a space of ground, to the O. Eng. plaec, Mid. Eng. pleck, later platch, patch. " Plot," in the sense of plan, scheme, would then be identical with " plot," a conspiracy, which may be a shortened form of " complot," a French word, also of doubtful origin, meaning in the 12th century " a compact body of men "; in the 14th century " conspiracy."
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)