At once and First

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

First and at once are semantically related. in immediately topic. In some cases you can use "First" instead the phrase "At once" as an adjective or an adverb, when it comes to topics like instantaneous.

First adverb - As a substitute.

At once and first are semantically related. Sometimes you can use "At once" instead the word "First" as an adjective or an adverb.

Nearby Word: firstly