One Breath
One Go, One Sitting
adverb
It's weird to think of having one energy. But, what gives you energy? You do it one time every couple of seconds. That would be taking breaths. So, "one energy" is one breath.
いっき
The reading is the same as the ones you learned with the individual kanji, though いち from 一 is shortened to いっ.
にがいくすりを一気にのみほしました。
I drank the bitter medicine down in one gulp.
元気そうな父のかおを見たら、一気に気がぬけました。
It was such a relief to see my father, who looked well.
僕のひいお婆さんは、ぎょう子を二百こ一気にたべた。
My great-grandma ate two hundred gyoza in one sitting.