Definitions
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. Plural form of cathetus.
from The Century Dictionary and Cyclopedia
 n. Plural of cathetus.
Etymologies
Sorry, no etymologies found.
Examples

Then, the height of the capital is to be divided into nine and a half parts, and down along the abacus on the four sides of the volutes, down along the fillet at the edge of the abacus, lines called "catheti" are to be let fall.

I learned something new today: a cathetus (pl. catheti) is a leg of a right triangle.
knitandpurl commented on the word catheti
"At point I, in the upper part of the quadrant, a tangent was made, and this—at points A and B—sprouted two metal abscissae, one parallel to line x and the other to line y. They intersected at point C inside the quadrant, thus giving the catheti of a right triangle whose hypotenuse was the segment AB in the tangent."
 The Golden Age by Michal Ajvaz, translated by Andrew Oakland, p 112 of the Dalkey Archive paperback
June 12, 2011