The meaning of "but or ever"

In this fragment from The Rime of the Ancient Mariner, what does but or ever mean?

I looked to heaven, and tried to pray;
But or ever a prayer had gusht,
A wicked whisper came, and made
My heart as dry as dust.

But and ever hold their usual meanings, the tricky one is 'or'. It would appear to be an archaic or dialectic form for 'before'

from Wiktionary

Preposition or

(now archaic or dialect) Before; ere.  

Quotation
1485, Sir Thomas Malory, Le Morte d’Arthur, Book VII: "Sey ye never so," seyde Sir Bors, "for many tymys or this she hath bene wroth with you, and aftir that she was the firste that repented hit."