carbuncle (n.) Look up carbuncle at
early 13c., "fiery jewel," from Old North French carbuncle (Old French charbocle, charboncle) "carbuncle-stone," also "carbuncle, boil," from Latin carbunculus "red gem," also "red, inflamed spot," literally "a little coal," from carbo (genitive carbonis) "coal" (see carbon). Originally of rubies, garnets, and other red jewels; in English the word was applied to tumors from late 14c.