Expressions (phrases, clauses, etc.), Adverb (fukushi)
immediately; instantly; with nary a pause; without a moment's delay
orig. read as 間（かん）、髪（はつ）をいれずsee 間髪入れず
間髪を入れず、迅速かつ的確な応対、畏れ入ります。Such an accurate, lightning-quick reply. What can I say?
Also written 間髪をいれず【かんぱつをいれず】、間髪を容れず【かんぱつをいれず】