directrix

[ dih-rek-triks, dahy- ]

noun

, plural di·rec·trix·es, di·rec·tri·ces [dih-, rek, -tri-seez, dahy-, dahy-rek-, trahy, -seez].

1. Geometry. a fixed line used in the description of a curve or surface.
2. Archaic. a directress.

directrix

/ daɪ-; dɪˈrɛktrɪks /

noun

1. geometry a fixed reference line, situated on the convex side of a conic section, that is used when defining or calculating its eccentricity
2. a directress

directrix

/ dĭ-rĕk′trĭks /

1. A straight line used in generating a curve such as a parabola.

Gender Note

See -trix.

Word History and Origins

Origin of directrix¹

From New Latin, dating back to 1615–25; direct, -trix

Word History and Origins

Origin of directrix¹

C17: New Latin, feminine of director

Example Sentences

The surface formed by revolving the catenary about its directrix is named the alysseide.

From Project Gutenberg

Since the tension is measured by the height above the directrix these two catenaries have the same directrix.

From Project Gutenberg

The only surface of revolution having this property is the catenoid formed by the revolution of a catenary about its directrix.

From Project Gutenberg

Hence T, the point of intersection of Pp and Qq, must be the centre of similitude and must be on the common directrix.

From Project Gutenberg

If the directrix, focus and eccentricity be given, we may employ the general method for constructing a conic.

From Project Gutenberg