Plain can refer to:
* Simple, unadorned, or lacking in features. (e.g., "She wore a plain white dress.")
* A level expanse of land. (e.g., "The plains of the Midwest are vast.")
Plane can refer to:
* A flat surface. (e.g., "The table top is a flat plane.")
* An aircraft. (e.g., "We took a plane to Hawaii.")