2. (Science: astronomy) The horoscope, or that degree of the ecliptic which rises above the horizon at the moment of one's birth; supposed to have a commanding influence on a persons life and fortune.
Hence the phrases to be in the ascendant, to have commanding power or influence, and lord of the ascendant, one who has possession of such power or influence; as, to rule, for a while, lord of the ascendant.
3. Superiority, or commanding influence; ascendency; 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)