in geometry, a line or radius falling perpendicularly on another line or surface; thus the catheti of a right-angled triangle, are the two sides that include the right angle.

CATHETUS of Incidence, in catoptries, a right line drawn from a point of the object, perpendicular to the reflecting line.

CATHETUS of Reflection, or of the Eye, a right line drawn from the eye perpendicular to the reflecting plane.

CATHETUS of Obligation, a right line drawn perpendicular to the speculum, in the point of incidence or reflection.

in architecture, a perpendicular line, supposed to pass through the middle of a cylindrical body, as a hall-futter, column, &c.