without a moment's delay; without even time to
Used adverbially to mean doing something immediately, or being so busy that one cannot spare time for something else. Often followed by a verb.
He started working without a moment's delay.
I was so busy that I worked without even time to eat lunch.
Variant using the kanji 無 for なく; slightly more formal or literary.
From 暇 (いとま, 'leisure time') + も (inclusive particle) + なく (adverbial form of ない, 'not'). Literally 'without even leisure time'.