noun, plural di·rec·trix·es, di·rec·tri·ces [dih-rek-tri-seez, dahy-, dahy-rek-trahy-seez] /dɪˈrɛk trɪˌsiz, daɪ-, ˌdaɪ rɛkˈtraɪ siz/.
- Geometry. a fixed line used in the description of a curve or surface.
- Archaic. a directress.
- geometry a fixed reference line, situated on the convex side of a conic section, that is used when defining or calculating its eccentricity
- a directress
- A straight line used in generating a curve such as a parabola.