一斉いっせい Common Adverb Noun English jmdict 1 adverb (fukushi)noun (common) (futsuumeishi) simultaneous;all at once
一斉送信いっせいそうしん Noun Irregular English jmdict 1 noun (common) (futsuumeishi) noun or participle which takes the aux. verb suru computing simultaneous transmission;sending to multiple recipients;sending a group message