1. Outspoken, without subtlety: The mayor was plain spoken and did not try to disguise what she was saying.
2. Descriptive of a lack in affectation; ordinary: Mildred's manners were plain and helped to make visitors very comfortable.
3. Not complicated: Celeste's mother preferred plain home cooked meals instead of highly spiced foods.
4. Pertaining to something simple; without ornament: The plain curtains in the window were strictly functional.

A wide and open stretch of land that is often treeless: The fields of wheat covered the plain as far as Josie could see.

1. An instrument or tool for making the surface of wood smooth: The cabinetmaker used a sharp plane to level the surface of the table made of pine.
2. A level of consciousness or development: Henry's plane of thought was lofty and purely academic.
3. A major supporting surface of an aircraft: The plane of the new airplane was designed to hold the wing and be strong but not heavy.
4. A word used interchangeably with "airplane": The plane taxied to the take-off site.

Flat, level; without depressions or elevations: The plane surface of the table was enhanced by the vase of stunning flowers.