What word describes someone who is stingy or miserly?

The term that accurately describes someone who is stingy or miserly is "parsimonious." This word conveys a sense of excessive reluctance to spend money or use resources, emphasizing a negative connotation associated with extreme frugality. A parsimonious person often hoards their wealth and tends to be overly cautious in their financial dealings, to the point of being miserable or not generous.

In contrast, the other terms—frugal, thrifty, and economical—generally have more positive connotations. "Frugal" suggests careful management of resources and spending wisely, but not necessarily to an extreme where one is unreasonably stingy. "Thrifty" refers to being economical but still has an implication of being smart with spending rather than merely tightfisted. "Economical" indicates being efficient in the use of resources, again without the negative implication of being miserly. Therefore, "parsimonious" is the term that most specifically aligns with someone exhibiting extreme stinginess.