expression
immediately; instantly; without a moment's delay
Rare variant of 間髪を入れず. Used in literary or emphatic contexts to mean 'without even a hair's breadth of pause'. Learners should prefer 間髪を入れず.
See also: 間髪を入れず
間一髪を入れず反撃に移った。
They immediately moved to counterattack without a moment's delay.
The standard, common expression with the same meaning. 間一髪を入れず is a rare variant that replaces 髪 with 一髪, possibly for emphasis.
A rare variant of 間髪を入れず, where 髪 (hair) is replaced by 一髪 (a single hair), intensifying the sense of 'not even a hair's breadth of interval'. The exact origin is uncertain, but it likely arose as an emphatic literary form.