The Spanish word 'puerto' comes directly from the Latin word 'portus', which meant 'harbor, port, or passage'. The Latin word underwent a common sound change as it evolved into Spanish, where the 'o' diphthongized into 'ue'. This same sound change pattern can be seen in many Spanish words that developed from Latin. The meaning remained largely unchanged, though in Spanish 'puerto' expanded to also specifically refer to a mountain pass, maintaining the core concept of a passage or point of transit.

Some related Spanish words include 'portuario' (relating to ports), 'aeropuerto' (airport - literally 'air port'), and 'portón' (large door or gate). These words all share the connection to the idea of passage or point of entry.

English speakers might recognize the connection to words like 'port', 'portal', and 'porch', which all come from the same Latin root 'portus'. Each of these English words maintains some connection to the original meaning of passage or entry: a 'port' is where ships enter and leave, a 'portal' is a gateway or entrance, and a 'porch' is an entrance structure to a building.