The word elliptical is derived from the oval shape known as an ellipse. Many comets have an elliptical orbit around the Sun that brings them closer at some times and farther away at others.
The adjective elliptical refers to the shape of an ellipse, which is an elongated circle, stretched into an oval. While it is a mathematical shape, it also is used to describe a way of speaking that cuts out extra, unnecessary language. When this style is used (say in a poem an elliptical style) — because it doesn't shed any light on the meaning — it sometimes makes the work obscure and hard to interpret.