1610s, American Spanish, "prairie; treeless, level plain," especially that of South America north of the Amazon, from noun use of Spanish llano "plain, even, level, smooth," ultimately from Latin planus "smooth, flat, level" (from PIE root *pele- (2) "flat; to spread"). Hence llanero "Latin-American cowboy" (1819), literally "plainsman."
"vast treeless plains of South America," 1704, from Argentine Spanish pampas, plural of pampa, from Quechua (Inca) pampa "a plain." Related: Pampean. Similar landscapes north of the Amazon are called llanos (see llano).
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."