Plans, Plains, and Planes
The three words in the headline for this post, and words derived from them—listed and defined below—stem from a common source.
Plan, plain, and plane all derive from the Latin adjective planus, meaning “clear,” “even,” “flat, level,” and “plain.”
Plan comes from the French word meaning “map”; the English word, originally a technical term in perspective drawing, soon came to apply to any diagram or drawing; usage was extended around the same time to refer to any set of details about a project or an event. The word also describes the action of preparing for a project or event. (A planform is the contour of a mass or object as seen from above.)
The adjectival use of plain stems from the Old French word meaning “even,” “flat,” and “smooth” and came also to mean “clear” or “evident” as well as “free from obstruction.” Later, additional senses of “ordinary,” “undecorated,” and “unattractive” joined those meanings. Idioms include “plain dealer,” meaning “one who is candid or honest,” “plain Jane,” for a woman of unprepossessing appearance, and “as plain as the nose on (one’s) face” as an expressive substitution for obvious. Plainclothes refers to a police officer in civilian clothing (plainclothesman was ubiquitous before female undercover police officers were common), someone who is plainspoken is frank, and a plainsong is a religious chant.
In Old French, plain also means “open countryside,” and it developed the sense of “level terrain” in English, originally in reference to Salisbury Plain. A floodplain is terrain built up by deposits of soil material caused by flooding or flat land susceptible to flooding.
To explain (the word, originally explane, literally means “make level”) is to make clear, but complain and complaint (and plaintive) are all unrelated, deriving from the Latin verb plangere, meaning “lament.”
Plane stems directly from Latin, and its use came about to distinguish what were originally both geometric and geographical senses of plain. Except for those who practice geometry or woodworking, it is best known as a truncation of airplane (originally aeroplane), which technically alludes to the aerodynamic wings of an aircraft rather than the entire structure. Biplane and triplane denote aircraft with two and three wings, respectively (generally stacked), not including smaller stabilizing wing structures. (Other specialized terms include seaplane and warplane.) To board a plane is to enplane (or emplane), exiting a plane is called deplaning.
In woodworking, a plane is a tool for smoothing surfaces, and to plane is to make level or smooth. As a verb, the word also denotes gliding or soaring or, in the case of a boat, skimming over the surface of water. (Hydroplane also serves for this meaning, especially in the context of powerboat racing, though the word also applies as a verb to any action of skimming over water.)
The name of the plane tree is unrelated, but planar means “two-dimensional” or “pertaining to a plane” and planaria is the designation for a genus of freshwater flatworms.
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