'ascertain' originates from Old French (Anglo-Norman), specifically the word 'acertener' (or 'acerter'), where the prefix 'a-' (from Latin 'ad-') meant 'to' and 'certain' (from Latin 'certus') meant 'sure'.

'ascertain' changed from Old French 'acertener' into Middle English forms such as 'ascerten'/'ascertainen' and eventually became the modern English word 'ascertain'.

Initially it meant 'to make certain or sure'; over time it evolved into the current common sense 'to find out for certain' or 'to determine/confirm something'.