Matte up is a term used to describe the action of making a shiny surface look dull or matte. It is commonly used in the context of photography, makeup, and graphic design. Some synonyms for matte up include: dull, tone down, reduce the shine, make less glossy, and soften the surface. These synonyms can be used interchangeably depending on the context and the degree to which the surface needs to be made matte. Matte up is a useful technique that can be used to provide a more subdued or natural look, and is often used in fashion and product photography to highlight the subject without the distraction of reflective surfaces.