The Oxford English Dictionary lists eight definitions of “ascendant” as a noun. They are grouped into two broad categories. The first four definitions are contained in a grouping with the heading “In senses belonging to, or derived from, astrology.” Definitions 5-8 belong to the second group entitled “In general senses.” There we find the following definitions and examples:

5. An upward slope, an acclivity, a rise; a flight of steps. Also fig. Obs., e.g. “A Lordly Ascendant..from Primate to Patriarch, and so to Pope.” [1641]

6. One who ascends or goes up. Obs., e.g. “That like the ascendants To the altar, by degrees, I thus approach you.” [1701]

7. That which rises above its surroundings; a summit or peak, e.g. “All the Capitals are Ascendents, so called because they stand higher than the Head-line of the Short.” [1676]

8. One who precedes in genealogical succession; an ancestor; a relative in the ascending line, whether lineal, as father, mother, or collateral, as uncle, great-uncle, e.g. “Their highest living ascendant, the father, grandfather, or great-grandfather.” [1861]

The numbers in brackets after the examples are the years given in the OED. In each instances I selected the most recent example that the OED supplies for a particular definition. We can infer from these examples that the term is largely obsolete (except for its astrological uses where it is still very much in use). But it does exist in the English language.