ab initio

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-.

1520s, "of or pertaining to a beginning," from French initial or directly from Latin initialis "initial, incipient, of the beginning," from initium "a beginning, a commencement; an entrance, a going in," noun use of neuter past participle of inire "to go into, enter upon, begin," from in- "into, in" (from PIE root *en "in") + ire "to go" (from PIE root *ei- "to go"). Related: Initially.