The term 'Plank Smoother' refers to a tool used in carpentry and woodworking. It is also known as a PLANE, which is a five-letter word that can be used to solve the crossword. A plank smoother is a hand tool used to smooth and shape wood surfaces. It consists of a flat metal blade with a handle attached to it. The blade is sharpened and used to shave off thin layers of wood, creating a smooth surface. The handle is used to guide the blade and provide leverage for the user.