adj

• (figurative) Controlling, dominant, surpassing.
  "In some cases the conquering state contented itself with imposing a tribute on the vanquished: who, being, in consideration of that burthen, freed from the expense and trouble of their own military and naval protection, might enjoy under it a considerable share of economical prosperity, while the ascendant community obtained a surplus of wealth, available for purposes of collective luxury or magnificence."
• (astrology) In an eastern direction rising just above the horizon.
  "This Phœbus promis'd, I forget the Year, / VVhen thoſe blue eyes firſt open'd on the Sphere; / Aſcendant Phœbus vvatch'd that hour vvith care, / Averted half your Parents ſimple Pray'r, / And gave you Beauty, but deny'd the Pelf / That buys your Sex a Tyrant o'er itſelf: […]"
• (astronomy) Rising towards the zenith.
  "[W]e muſt diſcover freezing ſtars that may reſolve the latter colds of vvinter, vvhich vvho ever deſires to invent, let him ſtudie the ſtarres of Andromeda, or the nearer conſtellation of Pegaſus, vvhich are about that time aſcendant."
• (botany, physiology) Of a part of an organism: synonym of ascending (“leading or sloping upwards”).
  "Artere ſouſclaviere. The aſcendant branch of the great Arterie."

noun

• (astrology, also figurative) The degree of the zodiac or point of the ecliptic which rises in an eastern direction above the horizon at a particular moment (especially the moment of a person's birth), which is supposed to have a commanding influence on a person's fortune and life; a horoscope.
  "[T]hey ſay that Jeſus in his natiuitie, had for his aſcendent, the ſigne of Virgo in her firſt face, as they terme it, […]"
• (by extension)
  "Towards the end of the session of 1836, the hopes of the Conservative party were again in the ascendant."
• (by extension)
  "One man has the ascendant over another."
• (by extension)
  "The Eſtate and Inheritance of a Perſon dying Inteſtate is, by Right of Devolution, according to the Civil-Lavv, given to ſuch as are ally'd to him ex Latere, commonly ſtiled Collaterals, if there be no Aſcendants or Deſcendants ſurviving at the time of his Death."