'certificado' originates from Spanish, ultimately from Latin 'certificatus', where 'certus' meant 'certain' and 'facere' (via '-ficare') meant 'to make or do'.

'certificatus' (Latin past participle formed from 'certificare') passed into Vulgar/Medieval Latin and Old Spanish as forms such as 'certificar' / 'certificado', eventually becoming the modern Spanish 'certificado'.

Initially it meant 'made certain' or 'that which makes certain'; over time it came to denote the document or act that provides official proof — the modern 'certificate' or 'certified'.