The Spanish word 'sínico' meaning 'relating to China' comes from the Latin word 'sinicus', which had the same meaning. The Latin 'sinicus' was formed by combining two parts: 'Sinae' (meaning 'China') and the suffix '-icus' (meaning 'relating to'). This Latin construction literally meant 'relating to China' or 'Chinese', and this meaning carried directly into Spanish.

A related Spanish word is 'sino' (meaning 'Chinese'), which shares the same Latin root 'Sinae'. Another related term is 'sinología' (meaning 'the study of Chinese language and culture').

In English, we can find several related words that come from the same Latin root 'Sinae', including 'Sino-' (as used in compounds like 'Sino-American' or 'Sino-Japanese'), and 'sinology' (the study of Chinese language, history, customs, and politics). The prefix 'Sino-' is commonly used in English to mean 'Chinese' or 'relating to China'.