/ əˈsesə(r); NAmE / noun
1.
an expert in a particular subject who is asked by a court or other official group to give advice
2.
a person who calculates the value or cost of sth or the amount of money to be paid :
an insurance / tax assessor
3.
a person who judges how well sb has done in an exam, a competition, etc. :
College lecturers acted as external assessors of the exam results.