'apriori' originates from Latin, specifically the phrase 'a priori', where 'a' meant 'from' and 'priori' (from 'prior') meant 'the former' or 'earlier'.

'a priori' entered English via Medieval/Neo-Latin philosophical usage; the Latin phrase was adopted into English technical and philosophical vocabulary without significant change in form, and is often used today either as two words ('a priori') or occasionally written as the single word 'apriori'.

Initially it meant 'from the earlier (preceding)', but over time it evolved into the technical philosophical sense 'known or justified independently of experience' and the broader sense 'assumed beforehand or deductively inferred'.