also: あっとゆうま · あっとゆーま
an instant; a split second; no time at all
Used to describe something happening extremely quickly, often in the phrase あっという間に (in the blink of an eye). The literal meaning is 'the time it takes to say ah!'.
See also: あっという間に
Summer vacation was over in the blink of an eye.
彼はあっという間にその問題を解いた。
He solved the problem in no time at all.