rectilinear

/ˌˈrɛktəˌlɪniər/

Other forms: rectilinearly

In math, a rectilinear shape is made up of straight lines. A square and a rectangle are both rectilinear.

Rectilinear is used to mean "straight," so if something moves in a straight line, it has rectilinear motion. A photographer's rectilinear lens reflects images accurately, so their straight lines don't appear curved. This word comes from the Latin root rectus, meaning "straight." In geometry, the meaning goes beyond that — a rectilinear polygon has straight sides that meet at a 90 degree angle. So from your geometry teacher's perspective, a rectangular speed limit sign is rectilinear but an octagonal stop sign is not.

Definitions of rectilinear

1. adjective

   characterized by a straight line or lines
   “rectilinear patterns in wallpaper”

   “the rectilinear propagation of light”

   synonyms: rectilineal

   linear, one-dimensional

   of or in or along or relating to a line; involving a single dimension