A line perpendicular to a surface (or line); in particular, either of the sides of a right triangle other than its hypotenuse
In a right triangle, the cathetus (plural, catheti) is either one of the two sides which, in a right triangle, are adjacent to the right angle. The remaining side, opposite the right angle, is called the hypotenuse. The cathetus is far more frequently known as a "leg" of the right triangle, or by the periphrasis "side about the right angle". When they are related to the hypotenuse, the catheti are often referred to simply as "the other two sides"
{i} line or radius falling perpendicularly on another; side of a right-angled triangle that makes a right angle with another one (Geometry)
One line or radius falling perpendicularly on another; as, the catheti of a right-angled triangle, that is, the two sides that include the right angle