To coarsen means to become rougher, cruder, or less refined. When your hands coarsen from working outside without gloves, the skin gets tougher and less smooth. When fabric coarsens after many washings, it loses its soft texture and feels scratchy.

The word also describes what happens to behavior, language, or culture when it becomes less polite or thoughtful. If someone's sense of humor coarsens, their jokes might become meaner or ruder. When public discussion coarsens, people start insulting each other instead of having respectful disagreements. A person's manners might coarsen if they stop caring about being considerate.

The opposite of coarsen would be to refine or polish something, making it smoother and more elegant. A woodworker might start with coarse sandpaper but switch to finer grades to avoid coarsening the wood's surface.

Think of coarsen as describing a process of deterioration or roughening, whether it's happening to a physical object like rope that coarsens from exposure to saltwater or to something less tangible like conversation that coarsens when people stop listening to each other carefully. The word coarse describes the rough state itself, while coarsen describes the process of becoming that way.