The Spanish word 'sobrino' (meaning 'nephew') comes from the Latin word 'sobrinus', which meant 'cousin' or more specifically 'sister's child'. The Latin term 'sobrinus' itself was formed by combining two parts: the word 'soror' meaning 'sister' and the suffix '-inus' which was used to show a relationship or connection. So literally, the word was built to mean 'someone connected to a sister'.

Over time, as the word evolved from Latin to Spanish, its meaning narrowed from referring to cousins or sister's children more generally, to specifically meaning 'nephew' in modern Spanish.

A related Spanish word is 'sor', which is used as a title for nuns (like 'Sister Mary'). This comes from the same Latin root 'soror' meaning 'sister'. While 'sobrino' refers to a sister's son (nephew), 'sor' maintains the direct connection to the concept of 'sister'.

The English word 'sorority' is related to 'sobrino', as it also comes from Latin 'soror' meaning 'sister'. A sorority is literally a sisterhood or an organization of sisters. Another related English word is 'sororicide', which means the killing of one's sister, following the same pattern as 'homicide' or 'fratricide'.