# directrix

[dih-rek-triks, dahy-] /dɪˈrɛk trɪks, daɪ-/
noun, plural directrixes, directrices
[dih-rek-tri-seez, dahy-, dahy-rek-trahy-seez] /dɪˈrɛk trɪˌsiz, daɪ-, ˌdaɪ rɛkˈtraɪ siz/ (Show IPA)
1.
Geometry. a fixed line used in the description of a curve or surface.
2.
Archaic. a directress.
Origin of directrix
1615-1625
1615-25; < New Latin; see direct, -trix
Usage note
See -trix.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2016.
Cite This Source
Examples from the Web for directrix
Historical Examples
• "You probably forget the important difference between a directrix and an axis," hotly observed Barbican.

Jules Verne
• directrix, a fixed line that is required for the description of a curve.

Various
• The centre of a circle is its focus, and its directrix has gone to infinity, having no special direction.

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

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

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

• As necessary as the directrix is to the curve, so are the corresponding laws to the State.

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

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

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

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
Word Origin
C17: New Latin, feminine of director
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Cite This Source
directrix in Science
 directrix   (dĭ-rěk'trĭks)    A straight line used in generating a curve such as a parabola.
The American Heritage® Science Dictionary
Cite This Source

### Difficulty index for directrix

Few English speakers likely know this word

### Word Value for directrix

0
20
Scrabble Words With Friends