a priori

"earlier; preceding, as in order of time," 1714, from Latin prior "former, previous, first;" figuratively "superior, better;" as a noun "forefather; superior rank;" comparative of Old Latin pri "before" (from PIE *prai-, *prei-, from root *per- (1) "forward," hence "in front of, before, first"). Also used adverbially (with to), by 1706.

17c., in reference to reasoning from a consequent to its antecedent, from an effect to its cause; Latin, literally "from what comes after;" from a "off, away from," usual form of ab before consonants (see ab-) + posteriori, neuter ablative of posterius, comparative of posterus "after, subsequent," from post "after" (see post-). Opposed to a priori. In modern use (from c. 1830, based on Kant) roughly equivalent to "from experience."

word-forming element meaning "away, from, from off, down," denoting disjunction, separation, departure; from Latin ab (prep.) "off, away from" in reference to space or distance, also of time, from PIE root *apo- "off, away" (also the source of Greek apo "off, away from, from," Sanskrit apa "away from," Gothic af, English of, off; see apo-).

The Latin word also denoted "agency by; source, origin; relation to, in consequence of." Since classical times usually reduced to a- before -m-, -p-, or -v-; typically abs- before -c-, -q-, or -t-.