That is the reflex orientation of a planet's birth position, as modernly used in the so-called Uranian Astrology, to the degree on the opposite side of the Cancer-Capricorn axis, of which the midpoint is either 0o Cancer or 0o Capricorn. For eg, at 14o Capricorn, the antiscion of a planet is at 16o Sagittarius, which point becomes successful when another planet, or one in transit, occupies it.
The concept is applicable to two planets which have the same declination on the same side of the equator, as first used by Ptolemy. One on the other side of the same downturn was called a contra antiscion.
