1540s, "plan of action, scheme, design;" 1550s, "ground-plan, drawing, sketch," senses now obsolete, from French plateforme, platte fourme, literally "flat form," from Old French plat "flat, level" (see plateau (n.)) + forme "form" (see form (n.)). These senses later went with plan (n.).
The sense of "raised, level surface or place" in English is attested from 1550s, especially "raised frame or structure with a level surface." Specifically in geography, "flat, level piece of ground," by 1813. The railroad station sense of "raised walk along the track at a station for landing passengers and freight" is from 1832.
The U.S. political meaning, "statement of political principles and of the course to be adopted with regard to certain important questions of policy, issued by the representatives of a political party assembled in convention to nominate candidates for an election," is from 1803. It is probably originally an image of a literal platform on which politicians gather, stand, and make their appeals, and perhaps it was influenced by the earlier sense in England of "set of rules governing church doctrine" (1570s). In 19c., platform was used generally in a figurative sense for "the function of public speaking," and even was a verb, "to address the public as a speaker."
late 13c. (c. 1200 as a surname), "thick board used in construction," from Old North French planke, a variant of Old French planche "plank, slab, little wooden bridge" (12c.), from Late Latin planca "broad slab, board," probably from Latin plancus "flat, flat-footed," from a nasalized variant of PIE root *plak- (1) "to be flat." Planche itself was also used in Middle English.
Technically, timber sawed to measure 2 to 6 inches thick, 9 inches or more wide, and 8 feet or more long. The political sense of "article or paragraph formulating a distinct principle in a party platform" is U.S. coinage from 1848, based on the double sense of platform. To be made to walk the plank, "be forced to walk along a plank laid across the bulwarks of a ship until one reaches the end and falls into the sea," popularly supposed to have been a pirate form of execution, is attested from 1789, and most early references are to slave-ships disposing of excess human cargo in crossing the ocean.
also *pletə-, Proto-Indo-European root meaning "to spread;" extension of root *pele- (2) "flat; to spread."
It forms all or part of: clan; flan; flat (adj.) "without curvature or projection;" flat (n.) "a story of a house;" flatter (v.); flounder (n.) "flatfish;" implant; piazza; place; plaice; plane; (n.4) type of tree; plant; plantain (n.2); plantar; plantation; plantigrade; plat; plate; plateau; platen; platform; platinum; platitude; Platonic; Plattdeutsch; platter; platypus; plaza; supplant; transplant.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit prathati "spreads out;" Hittite palhi "broad;" Greek platys "broad, flat;" Latin planta "sole of the foot;" Lithuanian platus "broad;" German Fladen "flat cake;" Old Norse flatr "flat;" Old English flet "floor, dwelling;" Old Irish lethan "broad."
1743, in architecture, "raised platform around an ancient arena" (upon which sat persons of distinction), also "projecting base of a pedestal," from Latin podium "raised platform," from Greek podion "foot of a vase," diminutive of pous (genitive podos) "foot," from PIE root *ped- "foot." Meaning "raised platform at the front of a hall or stage" is by 1947.
"raised platform from which a speaker addresses an audience or delivers an oration," especially in Christian churches, "the more or less enclosed platform from which the preacher delivers a sermon," early 14c., from Late Latin pulpitum "raised structure on which preachers stand," in classical Latin "scaffold; stage, platform for actors," a word of unknown origin.
Also borrowed in Middle High German as pulpit (German Pult "desk"). Sense of "Christian preachers and ministers generally" is from 1560s. Pulpiteer, old contemptuous term for "professional preacher," is recorded from 1640s.