The term ETCH-A-SKETCH PART is solved by the four letter word KNOB. The Etch-A-Sketch is a classic drawing toy that was first introduced in 1960. It consists of a flat gray screen in a red plastic frame, with two white knobs on the front for controlling the movement of a stylus. The knobs are used to draw lines on the screen, and can be twisted to erase them. The knobs are an essential part of the Etch-A-Sketch, as they are the only way to control the movement of the stylus.