The Spanish word 'centenario' (meaning 'centenary') comes from the Latin word 'centenarius' meaning 'relating to a hundred'. This Latin word was formed by combining two parts: 'centum' meaning 'hundred' and the suffix '-arius' meaning 'belonging to' or 'related to'. So literally, it meant something that belongs to or relates to a hundred, which evolved to specifically refer to a hundredth anniversary or a period of 100 years.

Some simpler related Spanish words include 'cien' (hundred), 'ciento' (hundred), and 'centena' (group of hundred). These all derive from the same Latin root 'centum'. The word 'centavo' (cent, one-hundredth) is also related, referring to one-hundredth of a monetary unit.

Several English words share this Latin ancestry, including 'century' (a period of 100 years), 'cent' (one-hundredth of a dollar), 'percent' (per hundred), and 'centennial' (occurring every 100 years). The English word 'centenary' is a direct cognate of Spanish 'centenario'. All these words preserve the core meaning related to 'hundred' from Latin 'centum'.