The term DARKEN, SAY can be solved by the three letter word DYE. Dyeing is a process of adding color to fabric or other materials such as leather, yarn, and paper. It is used to change the color of an item or to give it a more vibrant look. Dyeing is done by adding a DYE to the material, which then bonds with the fibers of the material. The process of dyeing can also be used to darken an item, making it appear darker than its original color.