Ascendant

n. [Fr. ascendant, n. & p. pr. of O. Fr. ascendre, Pr. ascendre, Lat. ascendere. See supra.] 1. Superiority, or commanding influence; as, one man has the ascendant over another. Chievres had acquired over the mind of the young monarch the ascendant not only of a tutor, but of a parent. Robertson.

2. An ancestor, or one who precedes in genealogy or degrees of kindred; a progenitor;—opposed to descendent; an heir in the ascending line. Ayliffe.
3. Height; elevation. [Rare.] “Sciences that were then in their highest ascendant.” Temple.
4. (Astrol.) The horoscope, or that degree of the ecliptic which rises above the horizon at the time of one's birth; supposed to have a commanding influence on a person's life and fortune.

Hence the phrases to be in the ascendant, denoting, to have commanding power or influence, and lord of the ascendant, denoting one who has possession of such power or influence; as, to rule, for a while, lord of the ascendant. Burke.