What does 一斉 mean?
一斉 is a Japanese noun meaning “simultaneous, all at once” in English. It is written as 一斉 in kanji, いっせい in hiragana, and issei in romaji. This word is part of JLPT N2 vocabulary.
Example sentence
生徒全員が一斉に立ち上がった。
All of the students stood up together.