early 15c., "to furnish with a floor," from floor (n.). Sense of "puzzle, confound" is from 1830, a figurative use, from earlier sense of "knock down to the floor" (1640s). Colloquial floor it "press down hard on the accelerator pedal of a motor vehicle" is by 1986 (compare earlier step on it in the same sense). In mid-19c. English university slang, it meant "do thoroughly and successfully" (1852). Related: Floored; flooring.
Old English flor "floor, pavement, ground, bottom (of a lake, etc.)," from Proto-Germanic *floruz "floor" (source also of Middle Dutch and Dutch vloer, Old Norse flor "floor," Middle High German vluor "floor, flooring," German Flur "field, meadow"), from PIE *plaros "flat surface" (source also of Welsh llawr "ground"), enlarged from root *pele- (2) "flat; to spread."
Meaning "level of a house" is from 1580s. The figurative sense in legislative assemblies (1774) is in reference to the "floor" where members sit and from which they speak (as opposed to the platform). Spanish suelo "floor" is from Latin solum "bottom, ground, soil;" German Boden is cognate with English bottom (n.). Floor-plan is attested from 1794; floor-board from 1787, floor-lamp from 1886, floor-length (adj.) of dresses is from 1910. The retail store's floor-walker is attested from 1862.
It forms all or part of: airplane; dysplasia; ectoplasm; effleurage; esplanade; explain; explanation; feldspar; field; flaneur; floor; llano; palm (n.1) "flat of the hand;" palm (n.2) "tropical tree;" palmy; piano; pianoforte; plain; plan; planar; Planaria; plane (n.1) "flat surface;" plane (n.3) "tool for smoothing surfaces;" plane (v.2) "soar, glide on motionless wings;" planet; plani-; planisphere; plano-; -plasia; plasma; plasmid; plasm; -plasm; -plast; plaster; plastic; plastid; -plasty; Polack; Poland; Pole; polka; protoplasm; veldt.
It is the hypothetical source of/evidence for its existence is provided by: Greek plassein "to mold," plasma "something molded or created;" Latin planus "flat, level, even, plain, clear;" Lithuanian plonas "thin;" Celtic *lanon "plain;" Old Church Slavonic polje "flat land, field," Russian polyi "open;" Old English feld, Middle Dutch veld "field."
1801, "a story of a house," from Scottish flat "floor or story of a house," from Old English flett "a dwelling, hall; floor, ground," from Proto-Germanic *flatja-, from suffixed form of PIE root *plat- "to spread." Meaning "floor or part of a floor set up as an apartment" is from 1824. Directly from flat (adj.) come the senses "level ground near water" (late 13c.); "a flat surface, the flat part of anything" (1374), and "low shoe" (1834).