'ratifier' originates from Old French 'ratifier' and ultimately from Latin 'ratificare', where 'rati-' (from 'ratus') meant 'calculated/firm' and 'facare/facere' meant 'to make'.

'ratifier' changed from Old French 'ratifier' (and Medieval Latin 'ratificare') and passed into Middle English (as forms related to 'ratify') before becoming the modern English noun 'ratifier'.

Initially it meant 'to make firm, to confirm', and over time this developed into the noun sense 'a person or body that gives formal approval'.