The Spanish word 'monóxido' (monoxide) is constructed from three elements, all with ancient Greek and Latin roots. The prefix 'mono-' comes from the Greek 'μόνος' (monos) meaning 'alone' or 'single'. The middle element 'oxi-' derives from the Greek 'ὀξύς' (oxys) meaning 'sharp' or 'acid', which evolved to refer to oxygen in modern chemical terminology. The suffix '-ido' comes from the Latin '-idus', which indicated a perceptible quality, and in modern Spanish is used specifically as a chemical compound suffix.

These elements combined to create 'monóxido', literally meaning a compound with a single oxygen atom, which is exactly what a monoxide is in chemistry.

Several common Spanish words share these roots. The prefix 'mono-' appears in many simple Spanish words like 'monótono' (monotonous), 'monolingüe' (monolingual), and 'monopolio' (monopoly), all carrying the meaning of 'one' or 'single'. The 'oxi-' element appears in words like 'oxidar' (to oxidize) and 'oxígeno' (oxygen).

English speakers will recognize many cognates using these same elements. The word 'monoxide' itself is identical in meaning to Spanish 'monóxido'. Other related English words include 'monotone', 'monopoly', and 'oxygen', all sharing the same Greek roots. The 'oxide' part appears in many English chemistry terms just as it does in Spanish.