Does a priori have an implied substantive?

1. What is the etymology of priori?
2. Is a priori Latin?

What is the etymology of priori?

Borrowed from Medieval Latin ā priōrī (“involving reasoning from cause to effect; from first principles”, literally “from the former”).

Is a priori Latin?

A priori, Latin for "from the former", is traditionally contrasted with a posteriori. The term usually describes lines of reasoning or arguments that proceed from the general to the particular, or from causes to effects.