How can tempura be written in Chinese character although its first form derived from Portugal?
Tempura is one of the signature Japanese food known widely around the world but not a dish that originated in Japan. The Portuguese first introduced the original form of tempura in the Muromachi Era (1336～1573) to Nagasaki.
What they brought to Japan was not named tempura, but most likely a form of fritter; the name tempura was only taken from their word “tempero”, meaning to cook in Portuguese.
Japanese managed to find phonetic equivalent in Chinese character. There are several theories to its naming. It is written “天麩羅”: 天=ten for masterless samurai, called tenjiku-rounin, said to first sell tempura off the streets, 麩=pu indicating flour, and 羅=ra meaning lightly battered.
This theory sounds most reasonable, but another says that a popular writer from Edo (now Tokyo) devised a word temfura which became tempura.
Temfura was meant to be a word-game because masterless samurai (ten=tenjiku-rounin) sells them here-and-there, or furafura (fura=furafura), which eventually became tempura. It sounds very likely that word-game loving people of Edo would come up with this name.
When cooking, there is a trick to deep-fry the tempura for its light and crisp bite. It is made by mixing flour and eggs, dipping seasonal vegetables and ingredients in it, then frying.
Rather un-Japanese thing to do to cook a very Japanese dish is to mix mayonnaise instead of eggs to prevent the cooked tempura to be greasy and beat. This allows for remaining moisture to be fried.
Although Japan was a closed country until late 19th century, Tempura is sign that Japan was still connected to the world and what gives culinary connection to Japan and rest of the world in the modern world.