The term 'PART OF A HALLOWEEN COSTUME' can be summarized by two crossword solutions: MASK (4 letters) and WIG (3 letters). A MASK is a covering worn on the face, typically for disguise or protection. Masks have been used since antiquity for both ceremonial and practical purposes. Wigs are head coverings made from human or synthetic hair, often worn to change one's appearance or to cover baldness. Wigs have been popular throughout history, especially in theatrical performances. Both masks and wigs are commonly used as part of Halloween costumes.