The Spanish word 'nono' has an interesting dual etymology, drawing from both Latin and Italian sources. From Latin, it comes from 'nonus' meaning 'ninth,' which contributed to one meaning of the Spanish word. The other meaning, 'grandfather,' comes from the Italian word 'nonno' meaning 'grandfather.' This dual origin explains why 'nono' can refer to either 'ninth' or 'grandfather' in Spanish, though the 'grandfather' meaning is more commonly used in modern Spanish.

Some related Spanish words include 'noveno' (ninth), which shares the same Latin root 'nonus.' The word 'abuelo' is more commonly used for grandfather in Spanish than 'nono,' though both terms exist.

While English doesn't have direct cognates for 'nono,' we can see related words in the numerical family: 'nine' and 'ninth' are conceptually related, though they come from Germanic rather than Latin roots. The Latin influence can be seen in English words like 'nonary' (relating to the number nine) and 'nonet' (a group of nine).