* Formal: The astronomer calculated the ellipse of the comet's orbit around the sun.
* Descriptive: The artist used an ellipse to create the illusion of depth in the painting.
* Technical: The engineer used an ellipse to represent the cross-section of the bridge's arch.
* Informal: I forgot to put the period at the end of my sentence; I guess you could call it an ellipse.
* Humorous: My plans for the weekend are still in the ellipse phase.
The specific usage will depend on the context of your sentence.