Definition of directrix in English:


Syllabification: di·rec·trix
Pronunciation: /diˈrektriks

noun (plural directrices /-trəˌsēz/)

A fixed line used in describing a curve or surface.
More example sentences
  • In the following, the feet of perpendiculars dropped from points A, B, etc. on the parabola to the directrix will be denoted A ’, B ’, etc.
  • The focus and directrix of a hyperbola were considered by Pappus.
  • The directrix is used in the construction, which follows, mutatis mutandis, the same course as the above construction in the case of the ellipse.


early 18th century: from medieval Latin, literally 'directress', based on Latin dirigere 'to guide'.

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