carbuncle: [13] Etymologically, a carbuncle is a ‘small piece of coal’. It comes ultimately from Latin carbunculus, a diminutive form of carbō ‘coal’ (source of English carbon). This reached English via Old French carbuncle. The Latin word had two main metaphorical meanings, based on the idea of a glowing coal: ‘red gem’ and ‘red inflamed spot’, both of which passed into English.
The latter achieved some notoriety in British English in the 1980s following a remark by the Prince of Wales in 1984 comparing a piece of modern architecture unfavourably to a ‘carbuncle’, although ironically from the 15th to the 17th centuries the word was used for ‘something of great splendour’. => carbon[carbuncle etymology, carbuncle origin, 英语词源]