Before and Once

Before adverb - So as to precede something in order of time.

Once is a synonym for before in precede topic. In some cases you can use "Once" instead the word "Before" as an adverb or an adjective, when it comes to topics like earlier, formerly, in the past.

Once adverb - At an earlier or previous time.

Before is a synonym for once in time topic. You can use "Before" instead the word "Once" as an adverb or an adjective, if it concerns topics such as precede, earlier, formerly, in the past.