(1) Moving in or forming a straight line. (2) Having many straight lines.
Example:
After admiring Frank Lloyd Wright's highly rectilinear buildings for years, the public was astonished by the giant spiral of the Guggenheim Museum.
Rectilinear is a term used widely in physics. Rectilinear motion is motion in which the speed remains constant and the path is a straight line. Rectilinear rays, such as light rays, travel in a straight line. Rectilinear patterns or constructions are those in which straight lines are strikingly obvious. The trunks of trees in a forest from a strongly rectilinear pattern.