an old chestnut a joke, story, or subject that has become tedious and boring as a result of its age and constant repetition.
☞ The most likely source for this sense of chestnut is in the following exchange between two characters, Zavior and Pablo, in William Dimond's play Broken Sword (1816): ZAVIOR…When suddenly from the thick boughs of a cork tree-PABLO. (Jumping up) A chesnut, Captain, a chesnut…Captain, this is the twenty-seventh time I have heard you relate this story, and you invariably said, a chesnut, until now.