"dominant power or influence, state of being in the ascendant," 1712; see ascendant + -cy.
Entries linking to ascendancy
ascendant adj.
late 14c., ascendent, in astrology, "rising over the horizon," from Latin ascendentem (nominative ascendans), present participle of ascendere "to mount, ascend, go up" (see ascend). The sense "moving upward, rising" is recorded from 1590s.
As a noun in astrology, "point of the ecliptic or sign of the zodiac which is on the eastern horizon at the moment of birth." The planet that rules the ascendant is believed to have predominant influence on the horoscope. Hence in the ascendant "ruling, dominant" (not, as is often thought, "rising"), 1670s, and the adjective meaning "superior, dominant," 1806.
-cy
abstract noun suffix of quality or rank, from Latin -cia, -tia, from Greek -kia, -tia, from abstract ending -ia (see -ia) + stem ending -c- or -t-. The native correspondents are -ship, -hood.
ascendance n.
1742, from ascend + -ance. According to OED, properly "the act of ascending," but used from the start in English as a synonym of ascendancy "state of being in the ascendant, governing or controlling influence."