General synonyms:
* Previously
* Earlier
* Formerly
* Prior to
* Ahead of
* In the past
* Hitherto
* Aforementioned (used to refer to something mentioned earlier)
* Aforetime (used to refer to a time in the past)
More specific synonyms:
* Antecedent (something that precedes something else)
* Preceding (happening or existing before something else)
* Precursor (something that comes before and indicates the coming of something else)
* Proleptic (referring to something that happens before it actually does)
Informal synonyms:
* Back in the day
* Once upon a time
* Way back when
The best synonym to use depends on the specific context and the desired tone.
Can you give me an example sentence of how you want to use "before" so I can help you find the perfect synonym?