Wikipedia lists “tenpura” as an alternative English spelling for tempura. Both forms represent the Japanese word for the battered and deep-fried dish, although “tempura” is overwhelmingly more familiar in English.
The spelling reflects romanization: Japanese writes the word as てんぷら, commonly rendered “tenpura.” In ordinary Japanese pronunciation, the nasal sound before the p can sound somewhat like an m to English speakers, which helps explain why “tempura” became the established English form. “Tenpura” preserves the spelling used in a straightforward romanization of the Japanese pronunciation.
Tempura usually consists of seafood or vegetables coated in a light batter and fried quickly in oil. It is often associated with Japanese cuisine, but its historical development includes influence from Portuguese-style frying techniques introduced to Japan in the sixteenth century. The alternate spelling is therefore a language and transliteration detail, not a different dish.