1. Someone whose job involves officially determining how much property is worth so it can be taxed according to its value: Mike's father has been a tax assessor for over ten years.
2. A person whose responsibilities are to give advice about some legal action to a judge or some other court official: The legal assessor was trying to find out why a police officer shot and killed an unarmed man several times.
3. Anyone who is officially evaluating how well someone did on a test, in some competition, etc.: The coach asked a well-known football assessor to help provide information as to why the school's team lost in the finals after never losing any other game during the year.