A more thorough explanation:

An adsessor is a person who helps a judge in a court of law. In ancient Rome, an adsessor was a legal assistant or adviser to a judge. In history, an adsessor was also known as an assessor, which was a title given to a master in chancery.

For example, if a judge needed help understanding a complicated legal case, they could ask an adsessor to assist them. The adsessor would provide advice and help the judge make a fair decision.