Definition

1. Noun:
   • A closed, oval-shaped plane curve: An ellipse is a geometric shape that resembles a flattened circle. It is defined as the set of all points for which the sum of the distances to two fixed points (called foci) is constant.

Usage

• The word ellipse is used primarily in mathematics, geometry, astronomy, and related technical fields to describe this specific shape.
• It is a countable noun (e.g., , ).

Examples

• Noun:
  • The orbits of planets around the sun are ellipses, not perfect circles.
  • She drew a perfect ellipse on the whiteboard to illustrate the concept.
  • The architect used an ellipse as the base shape for the building's design.

Advanced Usage

• "The foci of an ellipse": The two fixed points inside an ellipse used to define it.
  • In the diagram, points F1 and F2 are the foci of the ellipse.
• "The major/minor axis of an ellipse": The longest and shortest diameters of the ellipse.
  • The length of the major axis is twice the semi-major axis.

Variants and Related Words

• Elliptical (adj): Having the shape of an ellipse; or, in language, using an ellipsis (omission of words).
  • The room had an elliptical ceiling. (Shaped like an ellipse)
• Ellipsoid (n): A three-dimensional shape whose plane sections are all ellipses or circles.
  • The planet is not a perfect sphere but an ellipsoid.

Synonyms

• Oval: A more general, non-technical term for an egg-shaped or elongated round shape. Note: All ellipses are ovals, but not all ovals are mathematically perfect ellipses.

Notes on Different Meanings

• Ellipse vs. Ellipsis: Do not confuse ellipse (the geometric shape) with ellipsis (the punctuation mark "..." indicating an omission in text). They have different meanings and uses.

Noun

1. a closed plane curve resulting from the intersection of a circular cone and a plane cutting completely through it
   • the sums of the distances from the foci to any point on an ellipse is constant