The Japanese word for tomorrow is
明日

あした - ashita

Japanese Definition

tomorrow
1. 名詞. 明日。
Are you coming to tomorrow's party?
2. 名詞. 将来。
3. 名詞. ====連語====
4. 名詞. the day after tomorrow
5. 名詞. : あさって
6. 副詞. 明日に。
He'll be back tomorrow.
彼は明日帰ってくる。
7. 副詞. 将来に。
Wasting of the resources today will exterminate the human race tomorrow.
今日の資源の浪費が、将来、人類を根絶させることになる。

明日
1. n. (colloquial) tomorrow
明日は雨ですね。 - It seems like it will rain tomorrow.
明日の夕方 - tomorrow evening
2. n. (polite) tomorrow
3. n. the near future
4. n. (formal) tomorrow
5. n. (rare) tomorrow
6. n. Usage: Note that the pronunciation differs depending on register, which also happens for the antonym “yesterday” and the coordinate term “today”. Corresponding in formality to ashita, asu, and