Cathetus

In a right triangle, a cathetus (originally from Greek κάθετος, "perpendicular"; plural: catheti), commonly known as a leg, is either of the sides that are adjacent to the right angle.

In the context of the hypotenuse, the catheti are sometimes referred to simply as "the other two sides".

If they have different lengths, a distinction can be made between the minor (shorter) and major (longer) cathetus.

The ratio of the lengths of the catheti defines the trigonometric functions tangent and cotangent of the acute angles in the triangle: the ratio

In architecture, the term cathetus has been used for the eye of the volute.