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).