surname, from marshal (n.). The city in Texas, U.S., was named in 1841 for U.S. Supreme Court Chief Justice John Marshall (1755-1835). The Marshall Plan, "U.S. assistance to aid certain Western European nations recovering from World War II," is from 1947, named for its initiator, George C. Marshall (1880-1959), who was U.S. Secretary of State 1947-49. The Marshall Islands in the western Pacific were explored in 1788 by British naval captains John Marshall (1748-1819) and Thomas Gilbert, and named for the former (for the latter, see Kiribati). Related: Marshallese.
1728, "make a plan of; put on paper the parts, dimensions, and methods of construction of," from plan (n.). By 1737 as "to scheme, to devise ways and means for (the doing of something)." Related: Planned; planning; plans. Planned economy is attested by 1931. Planned Parenthood (1942) formerly was Birth Control Federation of America.
1670s as a technical term in perspective drawing; more generally by 1706 as "the representation of anything drawn on a plane; a drawing, sketch, or diagram of any object," from French plan "ground plot of a building, map," literally "plane surface" (mid-16c.), from Latin planum "level or flat surface," noun use of adjective planus "level, flat" (from PIE root *pele- (2) "flat; to spread").
The notion is of "a drawing on a flat surface." A doublet of plain via a later, learned French form. The meaning "scheme of action, formulated scheme for the accomplishment of some object or attainment of an end" is by 1713.
1716, "one who plans, a deviser or arranger," agent noun from plan (v.). Betjeman coined the derogatory variant planster in 1945. Meaning "book or device that enables one to plan" is from 1971.
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).