Formal:
* Parsimonious: This is a more formal and neutral term.
* Miserly: This implies extreme frugality, often to the point of being unwilling to spend money even on necessities.
* Close-fisted: This refers to someone who is unwilling to part with money.
* Cheap: This is a more informal and negative term.
Informal:
* Scrooge: This refers to someone who is extremely stingy and unwilling to spend money, even for charitable purposes.
* Tightwad: This is a casual term for someone who is unwilling to spend money.
* Penny-pincher: This refers to someone who is extremely careful with their money, often to the point of being considered stingy.
* Cheapskate: This is a derogatory term for someone who is unwilling to spend money.
The best synonym to use will depend on the specific context and the desired level of formality.