directrix

[dih-rek-triks, dahy-]

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.

Origin of directrix

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

Usage note

See -trix.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for directrix

Historical Examples of directrix

As necessary as the directrix is to the curve, so are the corresponding laws to the State.
The Romance of Mathematics
P. Hampson
Directrix, a fixed line that is required for the description of a curve.
The New Gresham Encyclopedia
Various
Similarly, in an hyperbola a vertex is nearer 704 to the directrix than to the focus.
Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6
Various
If a parabola roll on another parabola, their vertices coinciding, the focus of the first traces out the directrix of the second.
The Romance of Mathematics
P. Hampson
With your permission I will add a few words to those I have already uttered with regard to the directrix.
The Romance of Mathematics
P. Hampson

British Dictionary definitions for directrix

directrix

noun

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

Word Origin for directrix

C17: New Latin, feminine of director

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

directrix in Science

directrix

[dĭ-rĕk′trĭks]

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