The Spanish word 'júnior' comes directly from the Latin word 'iunior', meaning 'younger'. The Latin word underwent minimal changes as it entered Spanish, mainly adapting to Spanish spelling conventions with the addition of the accent mark over the 'u'. The meaning has remained essentially the same, referring to someone who is younger or more junior in position.

In Spanish, 'júnior' is a relatively straightforward loanword and doesn't have many etymologically related simpler Spanish words. It's commonly used in similar contexts to English, particularly in professional or familial settings.

The English word 'junior' is a direct cognate of Spanish 'júnior', as both come from the same Latin source 'iunior'. The words are nearly identical in both spelling and meaning, with English simply dropping the accent mark. In both languages, the word is commonly used to distinguish a younger person, particularly a son from his father of the same name, or someone of lower rank or seniority in a professional context.