The Spanish word 'vieja' (meaning 'old' when referring to a feminine subject) comes from the Latin word 'vetus' meaning 'old'. The Latin word first developed into the diminutive form 'vetulus' meaning 'somewhat old'. This then evolved into the Vulgar Latin 'veclus', which eventually became the Spanish masculine form 'viejo'. The feminine form 'vieja' was created by adding the feminine suffix '-a' to 'viejo'.

This evolution shows how Latin words often underwent sound changes as they developed into Spanish, with the 't' sound shifting to 'j' (pronounced like 'h' in modern Spanish) and the addition of gender-specific endings.

Some common related Spanish words include 'vejez' (old age), 'envejecer' (to grow old), and 'viejito/viejita' (diminutive forms meaning 'little old man/woman', often used affectionately). All these words share the same root and relate to the concept of age and getting older.

While English 'veteran' and 'inveterate' (meaning long-established or deeply ingrained) come from the same Latin root 'vetus', they took a different semantic path. Rather than simply meaning 'old', these English words developed to emphasize long-standing experience or persistent qualities. The connection can help English speakers remember that 'vieja' relates to age, just as a 'veteran' is someone with many years of experience.