prorsus

Prorsus is a worn-down pro versus, "turned forwards", and the oldest sense is spatial: straight ahead, without turning. That survives in prorsa oratio, forward-going speech, which is where the word prose comes from: language that walks on instead of turning back at the end of a line as verse does.

In practice you will meet it as an intensifier, utterly or absolutely, and with a negative as "not at all". The thing not to do is read the original sense into it and translate it as "then" or "next". Prorsus strengthens a statement, it does not order events. Beside it sits rursus, the same formation built on re-, "turned back", meaning again.