The term 'collar stiffener' refers to a device used to keep the collar of a shirt or blouse in place. It is usually made of metal or plastic and is inserted into the collar of the garment. The two crossword solutions for this term are 'STARCH' (6 letters) and 'STAY' (4 letters). STARCH is a substance that is often used to stiffen fabric, while a STAY is a piece of material that is sewn into the collar of a garment to help it keep its shape. Both STARCH and stays can be used as collar stiffeners.