What word refers to a sad or mournful expression?

The word "doleful" specifically conveys a sense of sadness or mourning. It derives from the Old English word "dol," which means grief or sorrow. When used to describe someone's expression, "doleful" suggests a deep, often poignant sadness that can be visually apparent in a person's demeanor.

In contrast, the other options all relate to positive emotions. "Joyful" and "cheerful" clearly denote happiness and positivity, while "ecstatic" implies an intense joy or excitement. These choices do not align with the sentiment of sadness or mourning, making "doleful" the only appropriate term to describe a sad or mournful expression.