Is it ensure, insure, or assure?
early 15c., "to fix the amount (of a tax, fine, etc.)," from Anglo-French assesser, from Medieval Latin assessare "fix a tax upon," originally frequentative of Latin assessus "a sitting by," past participle of assidere "to sit beside" (and thus to assist in the office of a judge), from ad- "to" (see ad-) + sedere "to sit" (see sedentary). One of the judge's assistant's jobs was to fix the amount of a fine or tax. Meaning "to estimate the value of property for the purpose of taxing it" is from 1809; transferred sense of "to judge the value of a person, idea, etc." is from 1934. Related: Assessed; assessing.