一気(いっき)にin one go, in one gulp, in one breath, without stopping, without pausing, without resting, in one sitting, at a stretch, all at once, immediately, instantly, right away, straight away, straightaway

一気(いっき)に仕事(しごと)をしたので、疲(つか)れました。

I am tired because I did all the work at once. {in one go, in one gulp, in one breath, without stopping, without pausing, without resting, in one sitting, at a stretch, all at once, immediately, instantly, right away, straight away, straightaway}

アルコールを一気(いっき)に飲(の)み干(ほ)すのは危険(きけん)です。

It is dangerous to drink alcohol all at once. {in one go, in one gulp, in one breath, without stopping, without pausing, without resting, in one sitting, at a stretch, all at once, immediately, instantly, right away, straight away, straightaway}

ラストスパートで、あるランナーが前(まえ)のランナーを一気(いっき)に抜(ぬ)いた。

In the final spurt, a certain runner overtook the runner in front all at once. {in one go, in one gulp, in one breath, without stopping, without pausing, without resting, in one sitting, at a stretch, all at once, immediately, instantly, right away, straight away, straightaway}

階段(かいだん)を一気(いっき)に駆(か)け上(あ)がったので、呼吸(こきゅう)が苦(くる)しくてしょうがないです。

Since I ran up the stairs all at once, I'm so out of breath that it's unbearable. {in one go, in one gulp, in one breath, without stopping, without pausing, without resting, in one sitting, at a stretch, all at once, immediately, instantly, right away, straight away, straightaway}

飼(か)い犬(いぬ)が家(いえ)の中(なか)を滅茶苦茶(めちゃくちゃ)に荒(あ)らした時(とき)、今(いま)までの不満(ふまん)が一気(いっき)に爆発(ばくはつ)しました。

When my pet dog wrecked the inside of the house, all my frustrations exploded at once. {in one go, in one gulp, in one breath, without stopping, without pausing, without resting, in one sitting, at a stretch, all at once, immediately, instantly, right away, straight away, straightaway}