Tesseract

In honor of Madeleine L'Engle's passing, I decided to jumpstart the Word Goober, a blog I reserved at least a year ago.

It's a term well known to fans of A Wrinkle In Time.

tes·ser·act n. The four-dimensional equivalent of a cube.

Wikipedia says:

In geometry, the tesseract, also called 8-cell or octachoron, is the four-dimensional analog of the (three-dimensional) cube, where motion along the fourth dimension is often a representation for bounded transformations of the cube through time. The tesseract is to the cube as the cube is to the square; or, more formally, the tesseract can be described as a regular convex 4-polytope whose boundary consists of eight cubical cells.

A generalization of the cube to dimensions greater than three is called a “hypercube”, “n-cube” or “measure polytope”. The tesseract is the four-dimensional hypercube or 4-cube.

According to the Oxford English Dictionary, the word tesseract was coined and first used in 1888 by Charles Howard Hinton in his book A New Era of Thought, from the Ionic Greek “τεσσερες ακτινες” (“four rays”), referring to the four lines from each vertex to other vertices. Some people have called the same figure a “tetracube”, and also simply a "hypercube" (although a hypercube can be a cube of any dimension).