A plane curve formed by the intersection of a right circular cone and a plane parallel to an element of the cone or by the locus of points equidistant from a fixed line and a fixed point not on the line.
[New Latin, fromGreekparabole, comparison, application, parabola (from the relationship between the line joining the vertices of a conic and the line through its focus and parallel to its directrix), fromparaballein, to compare; see PARABLE.]
(click for a larger image)parabola
Any point on a parabola is the same distance from the directrix as it is from the focus (F). AC equals CF and BD equals DF.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.