adjacent side | opposite side

A leg of a right triangle (i.e., a side adjacent the right angle) is also known as a cathetus (plural: catheti). While this usage is rather rare in English, the terms Ankathete (on-cathetus) and Gegenkathete (opposite-cathetus) are commonly used in German to denote the legs adjacent to and opposite the (non-right) angle in question, respectively. In general, a cathetus is a line falling perpendicularly on a surface or another line.

hypotenuse | leg | perpendicular | right triangle