The Spanish word 'fijo' meaning 'fixed' comes from the Latin word 'fixus', meaning 'fixed' or 'fastened'. This Latin word 'fixus' was derived from the Latin verb 'figere', which meant 'to fix' or 'to fasten'. The evolution from Latin 'fixus' to Spanish 'fijo' shows a common sound change where the Latin 'x' (pronounced like 'ks') became the Spanish 'j' sound.

Some related Spanish words include 'fijar' (to fix, to set), 'fijación' (fixation), and 'fijamente' (fixedly, steadily). All these words share the same Latin root and maintain the core meaning of something being fixed or fastened in place.

English speakers can easily remember 'fijo' by connecting it to several English words that come from the same Latin root, such as 'fix', 'fixed', 'fixture', and 'affix'. Notice how both the Spanish and English words maintain the basic meaning of securing or fastening something in place. The main difference is that English retained the 'x' sound from Latin while Spanish evolved it to a 'j' sound.