Costume accessories are items used to complete a costume, such as masks and wigs. The term 'costume accessory' can refer to a wide variety of items, including masks and wigs. In this case, the crossword solutions for the term 'costume accessory' are 'MASK' (4 letters) and 'WIG' (3 letters). Masks are often used to hide one's identity or to create a certain look, while wigs are used to change one's hair style or color. Both masks and wigs are popular costume accessories that can be used to enhance any costume.