'disappointer' originates from Old French/Middle English roots via the verb 'disappoint' plus the agentive suffix '-er'. The verb 'disappoint' comes from Old French 'desappointer', where the prefix 'des-' meant 'undo' and 'apointer' (related to 'appoint') meant 'to set a point or assign'.

'disappointer' developed by adding the agentive suffix '-er' to the verb 'disappoint'. The verb 'disappoint' passed into Middle English from Old French (desappointer / desapointer) and later became modern English 'disappoint'; applying '-er' produced the noun 'disappointer' meaning 'one that disappoints'.

Originally the Old French verb implied 'to undo an appointment' or 'to deprive of an office'; over time the sense shifted to 'to fail to satisfy or meet (hopes or expectations)'. Consequently, 'disappointer' now means 'one that causes disappointment'.