immediately; instantly; with nary a pause; without a moment's delay
運転手は間髪を入れずブレーキを踏んだ。
The driver hit the brakes without a moment's pause.
審判は間髪を入れずに笛を吹いた。
The referee blew the whistle without a moment's pause.
子供が転落しかけ、彼は間髪を入れず手を伸ばした。
As the child was about to fall, he reached out his hand without a moment's pause.