Word meaning before the Biblical Fall?

Prelapsarian is the usual term. I wouldn't say it is in daily use, but it is at least in non-theological dictionaries.

The word most like antediluvian but meaning not Before the Flood but Before the Fall would necessarily be antepeccant, which has the advantage of being somewhat adapted for English. However, the word most like antebellum would be antepeccatum. Both mean “before sin”.

Some might prefer to put a hyphen in that to make it ante-peccatum, just as one sometimes sees done with ante-bellum, ante-partum, and ante-jentacular.

But don’t expect to be understood by people who wouldn’t understand those last three, which is probably most people.

Oh sure, those familiar with the Augustine De Civitate Dei or Fellini’s Mens Augustini De Statu Creaturae Rationalis Ante Peccatum will know exactly what you mean. But quite honestly, how many of those sorts are you likely to encounter?