coarse
Rough in texture or not gentle and polite.
Coarse means rough in texture or lacking refinement. When you touch coarse sandpaper, it feels scratchy and rough against your skin, unlike smooth paper. Coarse fabric like burlap has a rough, bumpy texture compared to soft cotton or silk. Salt comes in different grades: fine salt dissolves quickly, while coarse salt has larger, rougher crystals.
The word also describes something crude or rude in manner. Coarse language includes vulgar words or rough expressions that polite people avoid. Coarse jokes are crude and inappropriate. When someone uses coarse manners, they act without consideration for others' feelings or social expectations.
Notice that coarse is the opposite of fine in both senses. Fine sand feels smooth and powdery; coarse sand feels gritty. Fine behavior shows thoughtfulness and refinement; coarse behavior lacks grace.
Don't confuse coarse with course, which sounds identical but means something completely different: a path, a class you take, or part of a meal. When you write about rough texture or crude behavior, you want coarse with an “a.”