The Spanish word 'plano' comes directly from the Latin word 'planus', which meant 'flat, level, or plain'. This word has maintained its core meaning remarkably well over time, as 'plano' in Spanish similarly means 'flat' or 'plane'.

Several common Spanish words share this Latin root, including 'planear' (to glide or to plan), 'planicie' (plain, flat land), and 'explanada' (esplanade, level ground). All these words maintain a connection to the concept of flatness or levelness.

English speakers can easily remember 'plano' by connecting it to several English words that come from the same Latin root: 'plane' (as in airplane or a flat surface), 'plain' (a flat area of land), and 'plan' (originally referring to a flat drawing). The word 'planar', meaning two-dimensional or flat, is also directly related. Even the word 'explanation' (literally, to make something 'plain' or clear) shares this ancient root.