If someone's behaviour or speech coarsens or if they coarsen it, they become less polite or they begin to speak in a less pleasant way. Her voice has deepened and coarsened with the years He had coarsened his voice to an approximation of Cockney
If something coarsens or is coarsened, it becomes thicker or rougher in texture. Skin thickens, dries and coarsens after sun exposure. his gnarled, coarsened features