directrix

/dəˈrɛktrɪks/
noun
  1. In geometry, a fixed line used to define a conic section (such as a parabola, ellipse, or hyperbola). The distance from any point on the curve to the focus is equal to the distance from that point to the directrix.
    • To graph the ellipse, we first located its two foci and the directrix.
    • The teacher drew the directrix as a straight line below the vertex of the parabola.
    • In a parabola, each point is the same distance from the focus and the directrix.
  2. A woman who directs or manages something; a female director or leader.
    • She served as the directrix of the community theater for over a decade.
    • The directrix of the research institute announced a new funding initiative.
    • As directrix of the choir, she led rehearsals with great enthusiasm.
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