Tempero, a Portuguese noun meaning condiment or seasoning, is a possible source of the word tempura.
The etymology of tempura is disputed rather than settled. One widely repeated explanation connects the Japanese word with Latin tempora, referring to periods such as Lent or the Ember Days when Portuguese missionaries ate fish or vegetables instead of meat. Another possibility is the Portuguese noun tempero, meaning a condiment or seasoning, or the related verb temperar, meaning to season.
The tempero theory is plausible because Portuguese cooks and missionaries had contact with Japan during the sixteenth century, especially around Nagasaki. Portuguese foodways included battered and fried vegetables such as peixinhos da horta, literally “garden fishes,” a dish often compared with tempura. Japanese could also have borrowed tempero with relatively little vowel change in pronunciation.
The culinary technique itself developed in Japan after those contacts and changed substantially. Early versions were associated with thicker, seasoned batter, while Edo-period tempura became lighter and focused on fresh seafood and vegetables. Thus, a Portuguese linguistic influence is possible without meaning that modern tempura is simply an unchanged Portuguese dish.