CATHETUS, 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 catoptrics, a right line drawn from a point of the object, perpendicular to the reflecting line.
CATHETUS of Reflexion, 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 reflexion.