Mannequin Toppers are a type of wig that is used to cover the head of a mannequin. They are typically made of synthetic fibers and come in a variety of colors and styles. The term 'Mannequin Toppers' is derived from the fact that they are placed on top of the mannequin's head, giving it a more realistic appearance. Wigs is the four letter solution for this crossword puzzle, which is an appropriate term for Mannequin Toppers as they are essentially wigs for mannequins.