Rectilinear means “made of straight lines” or “moving in a straight line.” It is a classroom and design word, not a kitchen word. A rectilinear building is all straight edges and sharp corners, no soft curves. Rectilinear motion in physics is movement along a straight path. Artists and architects use it for a look that is ruled, boxy, geometric. It is close to rectangular, but not the same: rectangular names a four-sided right-corner shape; rectilinear is wider — any arrangement or path that stays in straight lines. A zigzag of straight segments is still rectilinear; a circle is not.