• synonyms


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

  • 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.

  • Similarly, in an hyperbola a vertex is nearer 704 to the directrix than to the focus.

  • If a parabola roll on another parabola, their vertices coinciding, the focus of the first traces out the directrix of the second.

  • With your permission I will add a few words to those I have already uttered with regard to the directrix.

British Dictionary definitions for directrix


  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
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Word Origin

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


  1. A straight line used in generating a curve such as a parabola.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.