also: かんはつをいれず
immediately; instantly; without a moment's delay
Literally 'without putting a hair's breadth in between'; used for actions that follow another with no gap in time. Often used in narrative or formal contexts.
He answered the question without a moment's delay.
A rebuttal came back instantly.
すぐに is a common, everyday word for 'immediately'. 間髪を入れず is more emphatic and literary, stressing zero gap.
即座に also means 'on the spot' or 'immediately', but 間髪を入れず emphasizes the absence of even a tiny pause.
Standard kanji spelling. The reading かんぱつ is more common than かんはつ.
Alternate reading かんはつ; less common but recognized.
Kana-mixed variant; いれず is often written in kana.
Alternate kanji for いれる; less common.
From the idiom 間髪を容れず (かんぱつをいれず), literally 'not even inserting a hair's breadth'. 間髪 (かんぱつ) means the space of a single hair, and 容れず is the negative of 容れる (いれる, 'to insert'). The phrase describes an action so immediate that not even a hair could be placed between events.