# 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/.
1. Geometry. a fixed line used in the description of a curve or surface.

2. Archaic. a directress.

## Origin of directrix

1
From New Latin, dating back to 1615–25; see origin at direct, -trix

See -trix.

## Words Nearby directrix

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

## How to use directrix in a sentence

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

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

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

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

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

## British Dictionary definitions for directrix

directrix

/ (dɪˈrɛktrɪks, daɪ-) /

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

## Origin of directrix

1
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

## Scientific definitions for directrix

directrix

[ dĭ-rĕktrĭks ]

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