A windmill part is the ROTOR, which has five letters. It is a cylindrical component that rotates and is connected to an axle. Another windmill part is the VANE, which has four letters. This is a flat surface that is attached to the ROTOR and is used to catch the wind. The last windmill part is the BLADE, which also has five letters. This is a curved surface that is attached to the ROTOR and is used to capture the wind's energy.