planar

What it means

1. Of or pertaining to a plane.

   A planar projection of a three-dimensional object is its projection onto a plane.

2. Flat, two-dimensional.
3. graph theoryAble to be embedded in the plane with no edges intersecting.

   A complete graph with more than four nodes is never planar.

In a sentence

A planar projection of a three-dimensional object is its projection onto a plane.

Where it comes from

1. Proto-Indo-European*pleh₂-“flat”
2. Latinplānus“flat”, “level”
3. Late Latinplānārius“relating to a plane”
4. Englishplanar

From Late Latin plānārius (“relating to a plane”), derived from Latin plānus (“flat”, “level”), equivalent to plane + -ar, ultimately from Proto-Indo-European *pleh₂- (“flat”).