Dictionary/一斉いっせいIsseiJLPT N2一斉 (Issei) is a Japanese adverb meaning “simultaneous, all at once”.Meaningsadverb, nounsimultaneous; all at onceKanji in 一斉一one斉adjustedRelated words一寸a little一緒にtogether (with)一one一つone一one一同all present一番number one一人one person第一first一体(what) the heck一緒(doing) together一度once