The Portuguese, Spanish, and French words for bread, among others, all derive from Latin. The Spanish, Portuguese, Dutch, and British all made expeditions to Japan during the 1500s-1600s, at which point they introduced various Western concepts like bread, matchlock rifles, and Christianity. The Japanese word for this "Western" bread was naturally derived from either the Portuguese "pao" or the Spanish "pan."

As a parallel, the Portuguese introduced a tasty sweet spongey cake to the Japanese, known as "bread from Spain," or "Pao de Castela," referring to the Kingdom of Castille that was the bulk of Spain. The Japanese adapted the name "Castella" to the cake which it is known as to this day.

This is not the case with all similar words, however. The Portuguese "Obrigado" and the Japanese "Arigato," both meaning thank you, have completely dissimilar roots-the Japanese "arigato" is simply a polite form of "arigatai" whereas the Portuguese word shares the Latin root that English words such as "obliged" derive from.