The line separating the numerator from the denominator, whether horizontal, (sometimes proscribed) oblique, or diagonal.
A line or plane that is perpendicular to another.
A device such as a plumb line that is used in making or marking a perpendicular line.
at or forming a right angle (to something).
Exactly upright; extending in a straight line toward the centre of the earth, etc.
Independent of or irrelevant to each other; orthogonal.