Origin: Latin suffix -ular
Rectangular has 3 different meanings across 1 category:
having a set of mutually perpendicular axes; meeting at right angles
"wind and sea may displace the ship's center of gravity along three orthogonal axes"
"a rectangular Cartesian coordinate system"
Having a shape like a rectangle.
"The table has four right angles and opposite sides of equal length, making it rectangular."
In plain English: Rectangular means having four sides where opposite ones are equal and all corners form perfect right angles, just like a standard piece of paper or a brick wall.
"The garden is arranged in a large rectangular shape with straight paths on either side."