Origin

This character combines the metal radical on the left, which signals that the word relates to metal tools or metal properties, with a sound-hint component on the right that suggests the pronunciation "ton" or "dun". The pairing makes sense because a dull or blunt tool—especially a metal blade or edge that has lost its sharpness—is a practical problem in metalworking and daily use. Over time, the character extended from the concrete idea of a blunt metal tool to the broader meanings of slowness, dullness of mind, and lack of sharpness in general.