At once and Away

At once adverb - Without delay or hesitation; with no time intervening.

Away and at once are semantically related. in immediately topic. In some cases you can use "Away" instead an adverb phrase "At once", when it comes to topics like directly, presently, right now.

Away adverb - From this or that place.

At once and away are semantically related. Sometimes you can use "At once" instead an adverb "Away".