To separate into parts and disappear; to waste away; to scatter; to disperse; to vanish; as, a fog or cloud gradually dissipates before the rays or heat of the sun; the heat of a body dissipates
When something dissipates or when you dissipate it, it becomes less or becomes less strong until it disappears or goes away completely. The tension in the room had dissipated He wound down the windows to dissipate the heat