Why is the ninth month called September?
word-forming element meaning "away, from, from off, down;" from Latin ab-, ab "off, away from," from PIE root *apo- (see apo-). Reduced to a- before -m-, -p-, or -v-; sometimes abs- before -c- or -t-.
Away from: abaxial.
Used to indicate an electromagnetic unit in the centimeter-gram-second system: abcoulomb.