'assessorship' originates from English, formed by combining 'assessor' + the suffix '-ship'. 'assessor' itself derives (via Medieval Latin and Old French) ultimately from Latin 'assessor', related to the verb 'assidere' where 'ad-' meant 'to, toward' and 'sedēre' meant 'to sit'.

'assessorship' developed in English by adding the productive Old English/Old Norse/Germanic-derived suffix '-ship' (meaning 'state, office, condition') to the noun 'assessor' (a borrowing from Medieval Latin/Old French), yielding the modern term 'assessorship'.

Initially associated with the idea of 'sitting beside' (a helper or counselor who sits with a judge), the term evolved into the specialized modern sense of 'the office, duties, or tenure of an assessor.'